What Are the Different Magnifications of Objective Lenses? - magnifying power

 2024-10-10 17:02:28

I think you kind of skimmed over this point as if its nothing, but lets be serious here this is a major issue if we are aiming to use an f/15 scope.

I suppose this is a good opportunity to poll the community for interest. Those who are interested, please chime in. This will help me plan my first build.

My take on this would be - get largest aperture that you can afford and comfortably mount and use and adjust your working resolution to range of 1-1.2"/px for best small galaxy captures.

Long focal lengthin mm

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Cmos binning is not the same as cc'd binning as it's all software based. It basically averages the pixel data or sums it up. Problem with that, the device still reads the pixels individually, so each pixel readout still has its own read noise. With ccds, all the binned pixels are read at once with only one read noise involved. So binning CMOS only really saves you disk space, because you can do it any time later after data acquisition instead of in camera.

Long focal lengthcanon

I was thinking more about things we cant help, like a gust of wind which will now scrap 18 minutes of data instead of 2.

Geeze, George… I wouldn’t know what to charge. It’s really not tough to assemble, but you might be a little challenged finding all the parts. If you haven’t checked out my thread on making a “Curing Jar”, do check it out. I provided some info on where to get the LEDs and the Jar, and duct tape and Aluminum foil are likely things you can find on your own. I don’t think I said anything about where to get a power supply to make it work, but if you can’t find one for yourself, I can help you out with this, too. Just let me know!

Most galaxies are very small in angular size - maybe dozen of arc minutes at most. That is about 700px or less across the image of galaxy if one samples at highest practical sampling rates for amateur setups - which is 1"/px.

Focal lengthof lens formula

I've had decent galaxy results from the Esprit 100; you don't really need that much focal length to get to a good sampling rate for galaxies: 1~1.5 arc seconds

Now onto mounts and guiding. Most mounts have periodic error that is order of up to 10 minutes or there about. That is full period, and half period - where mount takes to go from peak to peak is half that. We could argue that "road" from peak to peak is either a) smooth - making RA drift same for first two and a half minutes as for second two and a half minutes - then if you can image/guide for 2.5 minutes - you should be able to image whole 5 minutes without issues and by extension whole worm cycle as it is the same road in other direction or b) one of two parts is significantly steeper - so it can't be guided - then you would loose every other sub to not being able to guide. If that is not the case - and you don't loose subs - then you should be able to guide whole RA period - and if you can guide whole RA period - what stops you from guiding 2 consecutive periods?

A unit like this is definitely needed, especially for castable resins. It would be great if you can build a waterproof one that can hold oxygen-excluding liquid.

I am happy to tell you that the unit I am developing now will be compatible with wet curing through the use of a glass reservoir that we will specify, but not likely supply. The plan is for IP65 rating on all electronics, and this would cover the occasional spillage.

Best way to bin is to actually not bin at all - best way is to split your subs so that different pixels end up in different sub subs. This way you avoid any mathematical operations with pixels - you reduce sampling rate (because you leave every other or third pixel) but you end up with multiples of subs - as you've imaged for longer. This shows that there is really nothing is lost - it is pure trade off between sampling rate and SNR,

I agree with you on binning making up for speed and do that with mosaiced images every chance i get, but taking the focal ratio to an extreme is not at all as easy as just using a "faster" scope.

Ok, but no software in reality implements (that I know of) above approach, although I'm sure that PI script can be written, so next best thing is to simply bin each sub after calibration and before stacking - either average or sum will do, but take care to save each sub in 32bit floating point format to avoid loosing precision (you should do this anyway when calibrating).

Im imaging with an 8" f/4.4 newtonian with a paracorr, bringing the effective focal length to 1018mm at roughly f/5. With my IMX571 and its 3.76 micron pixels i get 0.76"/px, which i have not been able to make use of fully even under very good seeing.

Yeah for minimum fuss a frac every time for me. I spent a few years with the SCT & RC but my goal was an fully automated Obsy and unless you enjoy constantly tinkering .. which I did at first but it soon wore off.. stick with a frac. Once I had the Esprit 150 I wondered why I had wasted so much imaging time. Of course a frac will come with the weight and length requirements.. (oh and cost!) but it’s pretty much set and forget.

The beam divergence is the cone plane angle determined by the beam diameter in the far field. From: Defence Technology, 2021.

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With regards to UV curing ovens not being mass-market products, neither are desktop SLA printers, and I believe Formlabs are doing OK.

What isfocal lengthin photography

So binning CMOS only really saves you disk space, because you can do it any time later after data acquisition instead of in camera.

The OP said the above so here is what I have recently tried for imaging galaxies. Due to the small pixel size of most modern CMOS cameras are quite over sampled. After looking at the specs of my ASI

I have been imaging for over three years now, always with refractors and at the moment I have a roll off roof observatory, an EQ6-RPRO, a SW Esprit 100, an ASI294MC PRo and control it all with an ASI Air pro. I will move to NINA eventually but at the moment it just works! I would love a scope with a long focal length to go after some galaxies and the smaller deep sky objects but would appreciate some advice. I’ve looked at Newtonians, Cassegrain,s in all their formats but appreciate that collimation and other matters will come into play. If anyone has gone down this route I’d be pleased to hear from you.

I think a 1 meter focal length newtonian would work very nicely as a galaxy scope with your camera. Need to tend to its needs though, particularly in the stability, collimation, and coma correction department.

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V-Flash UV Curing Oven (3D Systems) V-Flash is no longer supported so you might find a secondhand V-Flash UV oven at a lower price: new $3000 (discontinued) used $999 http://www.ebay.com/itm/162050206604

In any case - I don't think that sub duration is very important issue. If one can't guide for 10-15 minutes, one should sort out that bit first before attempting to do close up galaxies.

The cameras are quite expensive IMHO, but their feature set makes up for it. The Pylon Viewer is great for setting up the camera initially, and ...

I think you kind of skimmed over this point as if its nothing, but lets be serious here this is a major issue if we are aiming to use an f/15 scope.

The first thing I did after ordering my Form 2 a couple weeks ago was to start looking around for a curing chamber. There are a lot of DIY and “nail salon” curing solutions out there, but nothing that I saw as a commercial unit.

Say we are imaging under decent skies with an f/5 scope and we swamp read noise x5 with a 2 minute sub, well now with the f/15 scope that turns into an 18 minute sub. How many off the shelf mounts can do that reliably even if we know how to make the most out of our guiding gear?

My take is imaging anything at over 1500mm won't gain you anything. Oversampling can help a little. The best case forward for large aperture scopes is you can reduce them so you can end up with relative light buckets. Refractors tend to be slow. Something like a sharpstar sca360 would be ideal although not cheap, or a fast newt. Edgehd scopes with reducers are also a good option especially since they can be converted to low fl light buckets via hyperstar. That's kinda the path I'm looking at myself down the road.

My preference overall would be for a large refractor, but unfortunately my current mini observatory won't cope with the length of anything over the 115mm scope I now use. I did buy a 130mm triplet - but it was about 2" too long😭

I should add, commercial units are in fact available, but they are up around $10k. They are super nice, but super expensive. A popular brand is Loctite and their parent company is Henkel I believe.

In any case - I don't think that sub duration is very important issue. If one can't guide for 10-15 minutes, one should sort out that bit first before attempting to do close up galaxies.

Now take any modern sensor that has more than 12MP - that is 4000x3000px or more, so you have 4000px/700px = ~x5 at least x5 larger sensor than you actually need in terms of pixels. You can bin x5 and you'll be still able to capture galaxy in its entirety + some surrounding space.

I agree with you on binning making up for speed and do that with mosaiced images every chance i get, but taking the focal ratio to an extreme is not at all as easy as just using a "faster" scope.

If I use my 8" Newt and its dedicated coma corrector, with my ASI2600 camera, it gives me a resolution of 1.02" per pixel. If I was to use 100mm refractor with a similar focal length, and therefore a similar pixel scale, would the bigger aperture of the Newtonian give me any benefit?

Long focal lengthphotography

I’m sure there’s a market for a “commercially available” curing box. But you can make the one I “designed” for about $50. It works good. it’s as large as the print volume of both the Form1 and Form2, It’s 20 or 24W of UV so it also warms the print while curing it, the LEDs are on the outside of a plastic/glass container so you can fill the container with water to cure anaerobically, and they’re low voltage LEDs so if you spill water you’re chances of electrocution are minimal.

Modern CMOS sensors have read noise in 1-2e range. That is at least x4 less then CCD sensor - so one would need to expose for x16 loner with CCD to reach the same level of "overwhelm" with sky noise. Indeed, back in the day, exposures of 20 or more minutes very fairly common (even half an hour or longer for NB imaging).

CCDs used to have very large read noise - like 7-8e and sometimes even more (very few models had read noise as low as 5-6e).

Only difference between software and hardware binning is level of read noise. With CCDs and hardware binning - you have the same read noise regardless if you bin or not, but with CMOS sensors "effective" read noise is increased by bin factor.

Interchangeable Mounts ; t4 lens mount. T4 Mount ; tx lens mount. Vivitar TX ; t-mount and t2 lens mount. T-Mount & T2. reg - 55mm. width 42mm. thread pitch .75mm.

100% effective Only difference between software and hardware binning is level of read noise. With CCDs and hardware binning - you have the same read noise regardless if you bin or not, but with

I even asked my account manager at Formlabs if one was in development and was told no, that most people are using the nail salon method with relative success. As a mechanical engineer, I want something a bit more reliable than the currently offered solutions.

It improves SNR by bin factor from recorded image - regardless of how read noise is treated. Once you have image - no matter how it was acquired - was it CMOS or CCD - software binning will improve its SNR by bin factor (if you bin x2 - you will get x2 improvement, x3 - x3 SNR improvement and so on).

I am trying to find a good commercially available UV curing chamber to cure parts coming off our Form 2. If anyone knows of a good quality chamber let me know. Thanks, Cody

Despite really liking the RC8, I must admit that the images from the 115mm triplet are probably as good, if not better. Obviously the RC is binned and marginally quicker, but above about 800mm FL seeing becomes the predominant factor. I am currently considering a 250mm F4 Newtonian to give speed and FL (possibly even a Nexus to give F3).

What isfocal lengthof lens

So for me its a bit too much resolution, but honestly im getting pretty close with BlurXterminator if the seeing was good so not a complete daydream to work at that resolution.

My take on this would be - get largest aperture that you can afford and comfortably mount and use and adjust your working resolution to range of 1-1.2"/px for best small galaxy captures.

I've also had imaging newtonians; entry level ones are a lot cheaper than RC scopes, you can't beat them on bang for your buck. 200pds or Quattro 8S can produce stunning results for the price.

Shortfocal length

I was thinking more about things we cant help, like a gust of wind which will now scrap 18 minutes of data instead of 2.

My take on this would be - get largest aperture that you can afford and comfortably mount and use and adjust your working resolution to range of 1-1.2"/px for best small galaxy captures.

Yes - you would produce the same quality image (in terms of SNR) in 1/4 of the time with Newtonian as you would with 100mm refractor. This is because you have x4 more light gathering area with 200mm of aperture versus 100mm of aperture.

This is something I'm looking into as well. I have a heq5 so looking at lighter options. I have been considering the Stellamira 125 which seems a low maintenance option compared with a RC or newtonian.

Please forgive me for intruding. Unlike nail spas, UV curing ovens just aren’t mass-market products so I really doubt anyone will be marketing them at commodity prices anytime soon. (Please, please prove me wrong!)

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Btw - bin x5 will make F/15 scope work as if it was F/3 scope - so what is the point in going for F/4 Newtonian scope when you can comfortably use compact Cass type - be that SCT, MCT, RC or CC and produce excellent galaxy image.

Fair means in this context not profiteering. I am happy to pay a quality price for a quality product. 10K for a tin box a, timer, fancy logo, and some UV tubes is probably over the top!

Well, that’s the bad news. I suspect it won’t be much use to you, but I am actively working with an electrical engineer on exactly what you (and me) are looking for. I don’t feel comfortable yet discussing this in detail on the forum, but I would be glad to discuss offline if you, or anybody else, are interested. I don’t expect to have anything ready to go for at least a couple months. What I do have though, will be well made, validated with Formlabs resins, simple, and very capable.

A very popular one with a longer focal length that I cannot remember having read any complaints about is Edge HD8. It is easy to collimate (look at a de-focused star and play with three screws on the secondary mirror) and I expect it to hold collimation well, especially in an obsy.

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Olly Penrice did an article a few years ago comparing the performance of large aperture moderate FL refractors with large aperture long FL reflectors for galaxy imaging, there wasn't a lot in it and the low maintenance advantage of the refractor won the day for me and I settled on an Esprit 150. As @Clarkey has stated, seeing is often the limiting factor, I would have made a different choice if my scope was going on top of a mountain in Atacama.

Focal lengthexamples

In principle - above three are equivalent bar some minute differences that have to do with interpolation when aligning the subs for stacking (mostly academic arguments - no practical difference).

UV Crosslinker ovens are very costly when new, but the prices plummet for secondhand machines because they’re relatively plentiful. (I guess biotech laboratories don’t like to buy them second-hand.) Unfortunately, most machines come with 254 nm or 312nm UV-B lamps. It’s probably not cost-effective to replace UV-B lamps, but a secondhand crosslinker might be worthwhile if it has 405nm UV-A (gallium) lamps, or maybe 365nm UV-A lamps.

Second benefit is that given same sky, same mount, same conditions - 8" would produce very slightly sharper image than 4" - if both scopes are diffraction limited (which might not be the case if you use CC for newtonian or field flattener for refractor).

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Fair is a very subjective term. I am still not 100% sure where pricing will land. I hoped to hit a sell price of $100, but that doesn’t appear to be realistic. My goal is lowest possible cost without sacrificing quality. So, I won’t add cost for pretty, or for bells and whistles. Just a simple reliable well built chamber with fixed wavelength, intensity, and temperature. I’ll commit to under $500, but now that I am in pretty deep it seems somewhere in the middle will work.

We have been using the one based on the LED chamber - sorry cant remember the original poster to give proper credit. However, instead of water, we place our objects under vacuum to exclude oxygen and that works really well to aid curing. 2016-06-23 13.47.33.jpg3264×2448 1.94 MB

But you certainly might find a bargain-priced secondhand UV oven, so let us compile a list of search terms and brand names.

Otoflash (EnvisionTec) EnvisionTec offers several models, but Otoflash is the only one whose name I can remember. (Sorry!) new $4500 http://3nitysupply.com/index.php?route=product/product&product_id=139 used ?

I understand those who desire very clear parts also cure underwater. I’m not convinced this is necessary, but my focus is on engineering properties, not aesthetics. The goal is the get the best.mechanical properties from the Formlabs resins.

I take this point but have little experience of binning with CMOS cameras. What's your view on how this should be done and how effective it is?

However - this does not make any difference on final result if you already expose to swamp the read noise at bin x1. When you bin and increase read noise - you also increase other noise source in the same manner so their ratio - or "by how much you swamp" the read noise with say sky noise - remains the same.

Thanks for the link. I wish I had seen that a couple weeks ago. I’ll have to take a closer look to make sure my project is still worth pursuing. I do not think the B9 has a heated chamber, and I can see the chamber is quite small. But, it looks like nice.

Stratagene Stratalinker 1800 US Oven (Agilent) Cross-linkers can be re-purposed as UV curing ovens, but the new $2100 (discontinued) used $950 http://www.labx.com/item/stratagene-stratalinker-uv-crosslinker-2400/1527177

I will second this, I have the at115edt and compared it with my rc6 at 1370mm on M33 and the at115 actually out resolves it. I get pretty decent seeing conditions here in SE Arizona since I'm at fairly high altitude, 4200ft (about 1300m). John Hayes who I very much respect as an astronomer, had his setup near Tucson and observed similar things, even when using pretty large aperture long fl scopes. Eventually he sent his kit to Chile to get full benefit from his scope.

Agree with your reasoning with the other things though, there is no difference in a 3 minute or 30 minute guide duration if we dont have external disturbances. Getting quickly off topic now though.

You might choose swamp factor of 3 over 5 or something like that and simply go with shorter subs if wind gusts are real concern. Alternatively - everyone likes lower read noise camera, so maybe they will keep reducing the read noise further

Binning is the same underlying procedure as stacking - which is in turn the same underlying procedure as longer integration.

CCDs used to have very large read noise - like 7-8e and sometimes even more (very few models had read noise as low as 5-6e).

I had the same thoughts until recently. But, a lot of galaxies have very dim outer arms, dust other stuff like jet streams that require either a lot of integration or fast optics. So a fast say 1300mm fl scopes is a great idea imo.

Just to clarify what I'm saying - you take one sub and you split it into 4 smaller subs - first containing odd, odd pixels (in x and y), second odd, even, third even, odd and fourth even, even (a bit like bayer matrix splitting). In both axis - in X and Y you have twice as few pixels so each new sub is half the height and half the width - sampled at twice smaller sampling rate - but you have x4 more sub to stack - which improves total SNR x2.