Im starting this topic as a genuine question I have currently.
In a world of lenses & telescopes what is the current optically sharpest telescope on the market that fits the sub 300mm specifications.
I am talking... full frame small pixels corrected & capable, amazing strehl widefield lens/telescope that produces pinpoint small stars across the entire field of view - basically only diffraction limited telescope by aperture.
Ideally something like this is a native focal lenght telescope that doesnt use a reducer to achieve its focal lenght.
Feel free to pitch more ideas as OTAs and etc.
Here is the list I came up with so far:
WO RC51 (FPL53) (sharp so far but not perfect on some copies)
WO RC61 (FPL53) (bigger than RC51 means more aperture and more achievable sharpness ?)
Borg55 (Canon Fluorite) (very niche, sometimes good sometimes bad - corners questionable)
Tak60CB (Fluorite) (its a tak, but who uses this with tiny pixels FF and pushes it to the limit especially with reducer)
WO Pleiades 68 (FPL53) ??? issues https://www.astrobin.com/forum/c/equipment-forums/william-optics-pleiades-68/william-optics-pleiades-68/?page=3
Canon/Nikon 200mm F/2 - (ED/SED) (unknown, stopped down ? )
Sigma 135 F/1.8 (FLD/SLD) poor quality until stopped to F5 which makes it pointless https://www.astrobin.com/forum/c/astrophotography/equipment/sigma-art-135mm-f18/
Askar FRA300 (undisclosed) - softer than RC51/61
Canon 400mm F/2.8 (Canon Fluorite, ED) etc., used on Dragonfly array- focal lenght too big  |
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andrea tasselli:
Nikon AF-S 300mm VR
From images on astrobin this is far from sharp unfortunately.
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Luka Poropat:
From images on astrobin this is far from sharp unfortunately.
*Yeah? What about this: Nikon AF-S Nikkor 300mm F/2.8 ED Test - New (andrea tasselli) - AstroBin |
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It's hard to trust images on Astrobin, especially from lenses. A lot of the time those shooting with lenses are just starting out, or they have always used a lens/DSLR combo and have no sense for tilt/backfocus adjustment or other astrophotography related calibrations.
You may be looking for a unicorn, because lenses are still not designed with small pixel astronomy cameras in mind. This is how they can get away with only a few elements of quality glass in between all the different elements shoved into a lens.
In terms of telescopes that meet your description, you have pretty much listed all the ones that I can think of.
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andrea tasselli:
Luka Poropat:
From images on astrobin this is far from sharp unfortunately.
*Yeah? What about this: Nikon AF-S Nikkor 300mm F/2.8 ED Test - New (andrea tasselli) - AstroBin
Unfortunately still not sharp, you can see right edge of the field weird star shapes/halos around the stars (if thats not just post processing artifact) and thats on an APS-C sensor size.
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What about FSQ85 with new QB 0.73 reducer? - 330mm
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Seung-Jun Kim:
FSQ85 with 0.73 reducer - 330mm
Reducer causes all sorts of issues, also not suitable for small pixels. Most Taks were designed/made where 5+um pixels were a thing and it was easier on the optics. Nowadays its much harder to achieve great optical performance on a sensor like IMX455.  |
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Luka Poropat:
Unfortunately still not sharp, you can see right edge of the field weird star shapes/halos around the stars (if thats not just post processing artifact) and thats on an APS-C sensor size.
*With a median FWHM of 1.8 pixels (IMX571) is as sharp as it gets at full aperture. The aesthetic doesn't really enters the equation (halos and such). I don't have a FF sensor for doing these tests reliably but there are links to them posted previously.
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andrea tasselli:
With a median FWHM of 1.8 pixels (IMX571) is as sharp as it gets at full aperture
I think you have been doing your math completely wrong, also from seeing that in your image description. To calculate for instance seeing or the resolution you are imaging at its FWHM x pixel scale in that image above its FWHM of 4.9", which for a sampling of 2.63"/px gives you a 12.887
When your scopes optical fwhm is like 1/4th your observed FWHM, your FWHM is accurate to the true seeing within like a percent.
Supposing there arent any significant tracking errors.
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Luka Poropat:
Seung-Jun Kim:
FSQ85 with 0.73 reducer - 330mm
Reducer causes all sorts of issues, also not suitable for small pixels. Most Taks were designed/made where 5+um pixels were a thing and it was easier on the optics. Nowadays its much harder to achieve great optical performance on a sensor like IMX455.
Takahashi has released a new reducer for the FSQ-85 that shows better results than the older QE version.
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Luka Poropat:
I think you have been doing your math completely wrong, also from seeing that in your image description. To calculate for instance seeing or the resolution you are imaging at its FWHM x pixel scale in that image above its FWHM of 4.9", which for a sampling of 2.63"/px gives you a 12.887
When your scopes optical fwhm is like 1/4th your observed FWHM, your FWHM is accurate to the true seeing within like a percent.
Supposing there arent any significant tracking errors.
FWHM is expressed in pixels so it is 4.7". Don't where you picked up your numbers.
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andrea tasselli:
Luka Poropat:
I think you have been doing your math completely wrong, also from seeing that in your image description. To calculate for instance seeing or the resolution you are imaging at its FWHM x pixel scale in that image above its FWHM of 4.9", which for a sampling of 2.63"/px gives you a 12.887
When your scopes optical fwhm is like 1/4th your observed FWHM, your FWHM is accurate to the true seeing within like a percent.
Supposing there arent any significant tracking errors.
FWHM is expressed in pixels so it is 4.7". Don't where you picked up your numbers.
I picked it up directly from your description. Where you clearly state : median FWHM is 4.9" with a sampling of 2.62"/px yields a total 1.8px which is inherently wrong because you did the math wrong, it should be the other way around 4.9x2.62=12.8 |
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Luka Poropat:
andrea tasselli:
Luka Poropat:
I think you have been doing your math completely wrong, also from seeing that in your image description. To calculate for instance seeing or the resolution you are imaging at its FWHM x pixel scale in that image above its FWHM of 4.9", which for a sampling of 2.63"/px gives you a 12.887
When your scopes optical fwhm is like 1/4th your observed FWHM, your FWHM is accurate to the true seeing within like a percent.
Supposing there arent any significant tracking errors.
FWHM is expressed in pixels so it is 4.7". Don't where you picked up your numbers.
I picked it up directly from your description. Where you clearly state : median FWHM is 4.9" with a sampling of 2.62"/px yields a total 1.8px which is inherently wrong because you did the math wrong, it should be the other way around 4.9x2.62=12.8
You should clearly check your math again 
Think of it in more logical way: with each pixel you catch 2.62", seeing is 4.9" - so how many pixels you need to cover 4.9"?
Is it 12.8 pixels or less then 2 pixels?
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Luka Poropat:
I picked it up directly from your description. Where you clearly state : median FWHM is 4.9" with a sampling of 2.62"/px yields a total 1.8px which is inherently wrong because you did the math wrong, it should be the other way around 4.9x2.62=12.8
Suit yourself...
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I have the FS-60CB for travel and attached to it a modded EOS R. I run it at native FL with an AsiAirP. It is a tiny and light-weight set-up that can go anywhere anytime (i have no images of it in my AB portfolio though).
If you also consider a class higher, an FSQ-85 is a great choice. I run it at native FL 455mm (i have several images in my AB portfolio).
Cheers, John
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Jure Menart:
Luka Poropat:
andrea tasselli:
Luka Poropat:
I think you have been doing your math completely wrong, also from seeing that in your image description. To calculate for instance seeing or the resolution you are imaging at its FWHM x pixel scale in that image above its FWHM of 4.9", which for a sampling of 2.63"/px gives you a 12.887
When your scopes optical fwhm is like 1/4th your observed FWHM, your FWHM is accurate to the true seeing within like a percent.
Supposing there arent any significant tracking errors.
FWHM is expressed in pixels so it is 4.7". Don't where you picked up your numbers.
I picked it up directly from your description. Where you clearly state : median FWHM is 4.9" with a sampling of 2.62"/px yields a total 1.8px which is inherently wrong because you did the math wrong, it should be the other way around 4.9x2.62=12.8
You should clearly check your math again
Think of it in more logical way: with each pixel you catch 2.62", seeing is 4.9" - so how many pixels you need to cover 4.9"?
Is it 12.8 pixels or less then 2 pixels?
Median FWHM of 4.9" is measured on a stacked image in a FWHME Eccentricity tool in PixInsight or a similar tool in another software and this number is not the seeing. The "seeing" is calculated by multiplying that Median FWHM with the resolution/sampling (calculated from pixel size on a camera and focal lenght of the telescope/lens).
And just by measuring the jpeg on astrobin (which is not correct but as an example) his Median FWHM is 2,509px and multiplying that with his sampling of 2,59"/px its 6,5 which is still not even near the crazy 1.8 or 1.6 values Andrea is talking about.
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AdrianC.:
https://store-eu.hasselblad.com/
Enjoy
Has anyone ever even tried this ?
And if not then why put it here without actual examples of images.
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Luka Poropat:
AdrianC.:
https://store-eu.hasselblad.com/
Enjoy
Has anyone ever even tried this ?
And if not then why put it here without actual examples of images.
well there's some images here https://www.hasselblad.com/inspiration/stories/teruyasu-kitayama-astrography/
A redcat or samyang (or Nikkor 300mm) lens is still better.
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meyer gorlitz 300/f4 . razor sharp to the edge,only you need to focus seperate on the blue or red area. https://vintagelens.nl/shop/lenses/m42/meyer-optik-gorlitz-orestegor-300mm-f4-0-n-o-s-m42/?aewcobtn=1 |
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Well, I ain't know shit about math, but I am quite familiar with rude poeple and you, my dear, do not invite to discussion at all.
cheers,
K
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Karl Theberge:
but I am quite familiar with rude poeple and you, my dear, do not invite to discussion at all.
My intention wasn't to be rude, but to ensure accuracy in our discussion. Precision matters in technical matters like this. If there's a mistake, it's important to correct it for the sake of clarity and understanding.
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8.03
7.56
0.00
7.67
0.90
3.58
0.90
7.78
4.02
2.81
1.43
