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Old 28-07-2017, 09:38 AM
glend (Glen)
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Widefield - Lenses or scopes

So what are the pros and cons of widefield equipment for DSLR imaging? Reading other threads seems to indicate that lenses can suffer from distortion, coma, and in some cases colour dispersion; where as they offer variable focal length and f stop within a single device. Widefield scopes (APO) seem to offer superior optics at least in terms of distortion, coma, and colour control, but usually have a fixed focal length.
Ultra wide field seems to be the domain of specialist lenses and are outside the scope of this question.

What do you use and why?
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Old 28-07-2017, 10:01 AM
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DJScotty (Scott)
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Hey there Glen.
I have experimented with camera lenses for astrophotography and i found 2 distinct disadvantages
1st is the star distortion due to the non circular shape of the diaphragm.
2nd is the pita to focus. I jimmied up a belt driven system using my moonlite focuser motor but it was not consistent.

Other things to consider is if a zoom lens is used the lens elements component moves around in the lens itself thus affecting the orthography of the sensor plane. (Hope i used the right word there! )
Having said all that i was using a sigma 150-500mm lens at 500mm. So these distortions were quite evident. Maybe not so much at shorter fl like 50mm.

My 5c.
Scott
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Old 28-07-2017, 10:09 AM
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xelasnave
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Fortunately I was happy with the lens that came with the canon but 55mm seemed best.
Maybe do some captures with what you have and pick out what defects you perceive and target a lens or scope that moves you past that problem.

Alex
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Old 28-07-2017, 10:17 AM
JA
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Quote:
Originally Posted by glend View Post
So what are the pros and cons of widefield equipment for DSLR imaging? Reading other threads seems to indicate that lenses can suffer from distortion, coma, and in some cases colour dispersion; where as they offer variable focal length and f stop within a single device. Widefield scopes (APO) seem to offer superior optics at least in terms of distortion, coma, and colour control, but usually have a fixed focal length.
Ultra wide field seems to be the domain of specialist lenses and are outside the scope of this question.

What do you use and why?
Hi Glen,

If you are referring to previous recent threads with photographic lenses that are wide-angle (say < than the film diagonal) and then really wide & also really/reasonably fast lenses, they are not that easy/inexpensive to make and hence are specialty / expensive and even then there are many competing variables for optimum performance:

Widest Angle of view vs
Largest Aperture vs
High resolution vs
High Contrast vs
Good combination of Contrast/Resolution (MTF performance) vs
Low Coma vs
Low aberration (typically barrel & spherical) distortion vs
Low Chromatic abberation vs
Size vs
Weight vs
Cost

But there are many excellent choices out there, you just need to pick your acceptable compromises from the above


Best
JA
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Old 28-07-2017, 10:18 AM
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gregbradley
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I use mirrorless cameras and also permanently mounted telescopes with astro CCDs.

I can mount my mirrorless cameras on top of my telescope with a Losmandy D saddle. My mount is so strong it does not even notice the camera on top.

I have my camera mounted on an adjustable mounting unit I got off ebay for about $90. Its really well made, very solid, is about 100mm tall and is adjustable in all directions. A bit like a ball head but taller and more rigid and with a tightening knob for each type of adjustment.

I do this so I can point the camera up a bit so it does not take photos of the end of the scope! Taking the scope off is a 2 man operation hence I do it this way.

Lenses:
My Proline CCD is 36mm square so its going to really test out lenses.
Richard Crisp of the FLI Forum had a table that showed the back focus distance of various brand lenses. The Pentax 67 are one of the longest at about 85mm. So if you are using a CCD with a filter wheel you need to take that into account otherwise your lens will either be too close or too far and either won't focus or it will give bad stars in the corners.

Also to use on a CCD you need a manual aperture ring on the lens or an adapter that allows manual aperture control.

Of the Pentax 67 lenses I have tried the following:

Pentax 55mm not that great, coma needs to be stopped down. About $100
75mm F4.5 very good and great into the corners if stopped down a little around $125
165mm F2.8 this works wide open around $250
300mm F4 a fair bit of CA so stop it down or use it for narrowband. About $450

Pentax SMC Super Takumar lenses are also cheap and there are some great images around. Marc on this site has posted many great 100mm lens images with a QHY9.

I have also used:

Nikkor 50mm F1.8D very good, manual aperture ring. About $75
Nikkor 50mm F1.8G very good+ About $75
Nikkor 105mm F2.5 very good and cheap lens. About $125
Nikkor 180 F2.8 ED quite good some CA. About $500
Nikkor 85mm F1.8g a lot of CA about $550

Canon FD 85mm F1.8 CA not that great $75
Canon 24-70 F2.8L ii on a quick test it seemed very good. About $1600
Sony FE 24-70 F2.8 like the Canon above. $2800
Zeiss Loxia 21mm F2.8 utterly superb $1900
Zeiss Batis 25mm F2 some slight coma wide open but very useable and fast at f2, great colour. $1500
Sony Zeiss 55mm F1.8 fabulous stopped down. $800
Zeiss Batis 85mm F1.8 fabulous. $1750

I have used other older lenses like Minolta Rokkor 28mm Nikkor 24mm all no good.
Most of Fuji's lenses:

16-55 F2.8 is superb $1350
50-140 F2.8 is superb. $1600
14mm F2.8 is superb
I have the 10-24 F4 zoom but not tried it. Its probably very good.
Samyang 12mm F2 is very good and cheap about $400.


I have seen many images over the years and make a mental note of which equipment was used on the good ones.

Canon 200mm F2.8 lens seems very good.
Zeiss 135mm F2 APO is obviously fabulous - look at Troys amazing Milky Way images. About $2000
Samyang 135mm F2 is supposed to be almost as good if you believe that. About $600 new.

For UWA:
Nikon 14-24 about $1300 2nd hand
Samyang 14 2.8 if you can get a good one about $500 new
Irix 15mm F2.4 Firefly about $600 new
Sigma 14mm F1.8 Art $1959 appears to be the new king of the UWA.
Zeiss 15mm F2.8 $3000

Zeiss 300mm APO seems good, I imagine it costs a ton.

There are probably a few others I have tried but that is my experience so far.
The current popular lense seem to be the Samyang 135 F2. Its high performance and cheap. Its on my bucket list for portable tracker mirrorless imaging of Milky Way targets.

Greg.
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Old 28-07-2017, 11:01 AM
glend (Glen)
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Wonderful information Greg, thanks. Alot of the recent discussion on Milky Way, ie ultra wide field lenses covers that area. But what i was trying to ask was about equipment around the cross over pont between lenses and small APOs. For example scopes like the AT65EDQ, at 400mm focal length, or the TS Photoline 60mm at 330mm focal length, both of which have good optics and are very cost effective. Compared to the various DSLR lenses in that focal length reach.
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Old 28-07-2017, 07:40 PM
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gregbradley
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Quote:
Originally Posted by glend View Post
Wonderful information Greg, thanks. Alot of the recent discussion on Milky Way, ie ultra wide field lenses covers that area. But what i was trying to ask was about equipment around the cross over pont between lenses and small APOs. For example scopes like the AT65EDQ, at 400mm focal length, or the TS Photoline 60mm at 330mm focal length, both of which have good optics and are very cost effective. Compared to the various DSLR lenses in that focal length reach.
Just my opinion having seen many lens images of longer focal length they never seem to be as good as a telescope. One reason is they have many elements whereas a telescope only has 2 or 3 lenses. Camera lenses often have 13 elements most of which would be a basic type of glass.
The Pentax 67 300mm F4 EDIF was the closest to a telescope. Marco Lorenzi used one for quite a while very effectively but that was with a FLI Proline 16803 and a PME mount. An unusual setup but very effective.

Greg.
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Old 29-07-2017, 12:10 PM
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blink138 (Pat)
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Quote:
Originally Posted by gregbradley View Post
I use mirrorless cameras and also permanently mounted telescopes with astro CCDs.

I can mount my mirrorless cameras on top of my telescope with a Losmandy D saddle. My mount is so strong it does not even notice the camera on top.

I have my camera mounted on an adjustable mounting unit I got off ebay for about $90. Its really well made, very solid, is about 100mm tall and is adjustable in all directions. A bit like a ball head but taller and more rigid and with a tightening knob for each type of adjustment.

I do this so I can point the camera up a bit so it does not take photos of the end of the scope! Taking the scope off is a 2 man operation hence I do it this way.

Lenses:
My Proline CCD is 36mm square so its going to really test out lenses.
Richard Crisp of the FLI Forum had a table that showed the back focus distance of various brand lenses. The Pentax 67 are one of the longest at about 85mm. So if you are using a CCD with a filter wheel you need to take that into account otherwise your lens will either be too close or too far and either won't focus or it will give bad stars in the corners.

Also to use on a CCD you need a manual aperture ring on the lens or an adapter that allows manual aperture control.

Of the Pentax 67 lenses I have tried the following:

Pentax 55mm not that great, coma needs to be stopped down. About $100
75mm F4.5 very good and great into the corners if stopped down a little around $125
165mm F2.8 this works wide open around $250
300mm F4 a fair bit of CA so stop it down or use it for narrowband. About $450

Pentax SMC Super Takumar lenses are also cheap and there are some great images around. Marc on this site has posted many great 100mm lens images with a QHY9.

I have also used:

Nikkor 50mm F1.8D very good, manual aperture ring. About $75
Nikkor 50mm F1.8G very good+ About $75
Nikkor 105mm F2.5 very good and cheap lens. About $125
Nikkor 180 F2.8 ED quite good some CA. About $500
Nikkor 85mm F1.8g a lot of CA about $550

Canon FD 85mm F1.8 CA not that great $75
Canon 24-70 F2.8L ii on a quick test it seemed very good. About $1600
Sony FE 24-70 F2.8 like the Canon above. $2800
Zeiss Loxia 21mm F2.8 utterly superb $1900
Zeiss Batis 25mm F2 some slight coma wide open but very useable and fast at f2, great colour. $1500
Sony Zeiss 55mm F1.8 fabulous stopped down. $800
Zeiss Batis 85mm F1.8 fabulous. $1750

I have used other older lenses like Minolta Rokkor 28mm Nikkor 24mm all no good.
Most of Fuji's lenses:

16-55 F2.8 is superb $1350
50-140 F2.8 is superb. $1600
14mm F2.8 is superb
I have the 10-24 F4 zoom but not tried it. Its probably very good.
Samyang 12mm F2 is very good and cheap about $400.


I have seen many images over the years and make a mental note of which equipment was used on the good ones.

Canon 200mm F2.8 lens seems very good.
Zeiss 135mm F2 APO is obviously fabulous - look at Troys amazing Milky Way images. About $2000
Samyang 135mm F2 is supposed to be almost as good if you believe that. About $600 new.

For UWA:
Nikon 14-24 about $1300 2nd hand
Samyang 14 2.8 if you can get a good one about $500 new
Irix 15mm F2.4 Firefly about $600 new
Sigma 14mm F1.8 Art $1959 appears to be the new king of the UWA.
Zeiss 15mm F2.8 $3000

Zeiss 300mm APO seems good, I imagine it costs a ton.

There are probably a few others I have tried but that is my experience so far.
The current popular lense seem to be the Samyang 135 F2. Its high performance and cheap. Its on my bucket list for portable tracker mirrorless imaging of Milky Way targets.

Greg.
haha, any more greg?................... amazing!
pat
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