Advice: Looking for a Telescope or canon lens that can fit andromeda in frame

[Quetzalcoatl72]

I have a asi533 and I want to have large nebula(veil, north america, horsehead, eagle) and at least the whole of andromeda in frame with a budget of no more than £300, Can anyone recommend a telescope or canon lens with that budget thanks!

[iapa]

13 minutes ago, Quetzalcoatl72 said:

I have a asi533 and I want to have large nebula(veil, north america, horsehead, eagle) and at least the whole of andromeda in frame with a budget of no more than £300, Can anyone recommend a telescope or canon lens with that budget thanks!

A 200mm canon lens should be capable of that fov.

Or the Evoguide 50, 242mm f2 guide scope has good reviews.

 

You could also try using http://astronomy.tools/calculators/field_of_view/ calculator selecting various OTA/lenses

Edited June 3, 2021 by iapa

[Quetzalcoatl72]

14 minutes ago, iapa said:

A 200mm canon lens should be capable of that fov.

Or the Evoguide 50, 242mm f2 guide scope has good reviews.

 

You could also try using http://astronomy.tools/calculators/field_of_view/ calculator selecting various OTA/lenses

a guide scope that doubles as a good quality optic scope wouldn't be a bad idea thanks, tho they don't usually fit 2" adaptors so i'd need a 1.25 lp filter 😕

[iapa]

Just be aware that neither will give a flat field across the sensor.

The Evoguide is an apochromat. Backfocus is 60mm when you remove the extension to be to add your own DSLR camera adapter, 20mm is extension in place.

Spaces may be will needed.

[vlaiv]

Just a question, why do you need to do it in a single go?

You can always do mosaic.  APP (not sure if you managed to try it out and if you like it) - will stitch them for you if I'm not mistaken.

[The Lazy Astronomer]

13 minutes ago, iapa said:

Just be aware that neither will give a flat field across the sensor.

The Evoguide is an apochromat. Backfocus is 60mm when you remove the extension to be to add your own DSLR camera adapter, 20mm is extension in place.

Spaces may be will needed.

Skywatcher sell a flattener for the evoguide. It only has 17.5mm backfocus, but fortunately the OP has an asi533, so will be a perfect match and no additional spacers needed. 

[Quetzalcoatl72]

13 minutes ago, vlaiv said:

Just a question, why do you need to do it in a single go?

You can always do mosaic.  APP (not sure if you managed to try it out and if you like it) - will stitch them for you if I'm not mistaken.

never crossed my mind but it does seems more complicated. the closest I can get is my ed80 with a reducer, but I am not sure what reducer will work, it's almost in frame with a x0.50. do you know of any reducers?

[iapa]

https://www.firstlightoptics.com/pro-series/skywatcher-85x-reducer-flattener-for-ed80.html

 

[iapa]

SGPro will do your mosaics for you, as does NINA

 

[vlaiv]

32 minutes ago, Quetzalcoatl72 said:

never crossed my mind but it does seems more complicated.

It is a bit more complicated.

You need to create sequence of couple of tiles - as @iapa already said - capture software has features to help you create mosaics - you just say how you want to do it and they create sequence with coordinates and all. After that - stacking software should deal with stitching mosaics as well - at least I think APP does that for you.

I made couple of mosaics and I stitched those "by hand". That is a bit more involved, but it can still be done.

Other than taking more panels and stitching those after (and any binning involved if you want to image in same time as you would capture target with smaller scope) - it is pretty much the same as doing LRGB - there you also need to do multiple sets of subs in different filter - here you only reposition the scope between sets.

[nfotis]

With an APS sensor, you can use up to 400mm focal length in order to get a tight framing of Andromeda.

Another approach would be this: https://www.firstlightoptics.com/askar-telescopes/askar-fma180-f-4-5-astrograph-lens.html

Or a 300mm lens, if you are shooting with Canon lenses.

Check with the field of view calculator (select "Imaging mode"):

https://astronomy.tools/calculators/field_of_view/

N.F.

 

[vlaiv]

Problem with regular photo lenses is that they are not diffraction limited.

You can't hope to make very sharp Andromeda image with fast lens.

[Alien 13]

17 minutes ago, vlaiv said:

Problem with regular photo lenses is that they are not diffraction limited.

You can't hope to make very sharp Andromeda image with fast lens.

Daft question but how can you tell from the lens specification?

Alan

[Quetzalcoatl72]

8 hours ago, vlaiv said:

It is a bit more complicated.

You need to create sequence of couple of tiles - as @iapa already said - capture software has features to help you create mosaics - you just say how you want to do it and they create sequence with coordinates and all. After that - stacking software should deal with stitching mosaics as well - at least I think APP does that for you.

I made couple of mosaics and I stitched those "by hand". That is a bit more involved, but it can still be done.

Other than taking more panels and stitching those after (and any binning involved if you want to image in same time as you would capture target with smaller scope) - it is pretty much the same as doing LRGB - there you also need to do multiple sets of subs in different filter - here you only reposition the scope between sets.

could i not take a pic of half the galaxy and the other half after? and doing it in one night would be best, could be different seeing on the next night might make it off looking on one side

[vlaiv]

Just now, Alien 13 said:

Daft question but how can you tell from the lens specification?

Alan

I actually figured that out by measurement of really sharp lens, but I think you can figure it out from lens MTF.

Here is Samyang 135mm F/2 lens - generally accepted as very sharp lens for astrophotography.

You'll see that it has about 92-93% MTF at 30 lpmm. That is 33µm (1mm/30) pixel size and it will not be perfectly sharp.

MTF of ideal aperture looks like this:

X axis is sampling frequency and Y is contrast loss. This function is pretty much linear. That means that attenuation to 90% happens in first 10% of frequency (or lowest 10%). Since we want wavelength and wavelength is 1/frequency - 1/0.1 = 10. So sharpness falls to 90% at 10 times the size of max wavelength that aperture can support.

Say we want to compare that Samyang lens at F/2.8 (which people say is sharp) to ideal scope of same aperture. 135 / 2.8 = 48.2mm of aperture. At F/2.8 that corresponds to ideal pixel size of ~0.5µm for diffraction limited scope (critical sampling rate) - and x10 longer wavelength is 5µm.

Yet from above graph we see that 90% is already reached at 33µm - far sooner (with larger pixels) than it should happen for diffraction limited lens.

If you've ever read lens review - you'll notice that they mention F/8 to F/16 as being setting at which image starts to get softer due to effects of diffraction. Above calculation supports that - sharpness of the lens below about F/8 to F/16 is determined by lens itself and not by diffraction effects.

[vlaiv]

15 minutes ago, Quetzalcoatl72 said:

could i not take a pic of half the galaxy and the other half after? and doing it in one night would be best, could be different seeing on the next night might make it off looking on one side

Best approach for variety of reasons is to take all panels every night.

Imagine you image two nights and in first instance take half of galaxy on first night and half of galaxy on second night. It also happens that first night seeing is good and stars are tight and transparency is good, but on second night seeing is poor and transparency is poor. You'll be left with image that shows distinction both in sharpness and in signal to noise ratio - split in two.

If you image both parts on first night and both parts on second night - odds are that you'll average out both seeing effects and transparency issues. Image won't be as sharp as first night or as blurred as second night (and same goes for SNR) - but it will be the same average on both halves.

[Quetzalcoatl72]

4 minutes ago, vlaiv said:

Best approach for variety of reasons is to take all panels every night.

Imagine you image two nights and in first instance take half of galaxy on first night and half of galaxy on second night. It also happens that first night seeing is good and stars are tight and transparency is good, but on second night seeing is poor and transparency is poor. You'll be left with image that shows distinction both in sharpness and in signal to noise ratio - split in two.

If you image both parts on first night and both parts on second night - odds are that you'll average out both seeing effects and transparency issues. Image won't be as sharp as first night or as blurred as second night (and same goes for SNR) - but it will be the same average on both halves.

Never recorded anything over multiple nights, since my setup is never permanent I'd have to keep the camera in at all times when bringing the scope in i guess, keeping the same rotation, though i guess that doesn't matter as the sensor is square

Edited June 3, 2021 by Quetzalcoatl72

[iapa]

If tripod mounted, can you leave it out fully assembles with something like a telegizmo telescope cover.

After a session, if the mount supports it, home the telescope and then set hibernation mode. Put the cover on.

Next session all you need is to remove the cover, wake it up, and a quick PA check.

Other option if you take it in and out all the time, mark the ground where the tripod feet site, it will make PA easier when to take it all out again.

 

[vlaiv]

48 minutes ago, Quetzalcoatl72 said:

Never recorded anything over multiple nights, since my setup is never permanent I'd have to keep the camera in at all times when bringing the scope in i guess, keeping the same rotation, though i guess that doesn't matter as the sensor is square

There is very simple trick to orient camera the same every time. Just orient RA with either vertical or horizontal axis of the camera.

Place camera on the scope, aim at bright star and start exposure - then slew scope in RA direction for couple of seconds. Stop exposure. Exposure should have a line formed by star.

If line is horizontal or vertical (pick one - although for square sensor it does not matter) - you are done.  If not - rotate camera and repeat exposure until you get horizontal / vertical line.

With just a few corrections you'll get it aligned good enough.

Alternative is plate solving - it gives you camera orientation in degrees and you can rotate camera until you get orientation in degrees that matches previous session.

[Chris]

19 hours ago, iapa said:

Just be aware that neither will give a flat field across the sensor.

The Evoguide is an apochromat. Backfocus is 60mm when you remove the extension to be to add your own DSLR camera adapter, 20mm is extension in place.

Spaces may be will needed.

There is a flattener for the Evoguide. Both the Evoguide and flattener come in within the OP's budget. Also there shouldn't be any vignetting as the Flattener has a 28mm image circle and 533 sensor has a 16mm sensor on the diagonal. So in theory that could work.  

[Quetzalcoatl72]

20 hours ago, vlaiv said:

I actually figured that out by measurement of really sharp lens, but I think you can figure it out from lens MTF.

Here is Samyang 135mm F/2 lens - generally accepted as very sharp lens for astrophotography.

You'll see that it has about 92-93% MTF at 30 lpmm. That is 33µm (1mm/30) pixel size and it will not be perfectly sharp.

MTF of ideal aperture looks like this:

X axis is sampling frequency and Y is contrast loss. This function is pretty much linear. That means that attenuation to 90% happens in first 10% of frequency (or lowest 10%). Since we want wavelength and wavelength is 1/frequency - 1/0.1 = 10. So sharpness falls to 90% at 10 times the size of max wavelength that aperture can support.

Say we want to compare that Samyang lens at F/2.8 (which people say is sharp) to ideal scope of same aperture. 135 / 2.8 = 48.2mm of aperture. At F/2.8 that corresponds to ideal pixel size of ~0.5µm for diffraction limited scope (critical sampling rate) - and x10 longer wavelength is 5µm.

Yet from above graph we see that 90% is already reached at 33µm - far sooner (with larger pixels) than it should happen for diffraction limited lens.

If you've ever read lens review - you'll notice that they mention F/8 to F/16 as being setting at which image starts to get softer due to effects of diffraction. Above calculation supports that - sharpness of the lens below about F/8 to F/16 is determined by lens itself and not by diffraction effects.

I couldn't work out how to add lenses to Stellarium to see the field of view because it asks for aperture, that detail is never mentioned when looking at camera lenses, looking at these details you've provided I worked out that the current lens I have my eye on has an aperture of 50mm and that's the Canon EF 70-200mm F/4 L IS USM, does that sound pretty sharp to you? Than lens combined with the asi533 has andromeda in the perfect frame. The lens also can be zoomed in and out if I were to get something larger in the field. Thoughts?

[wulfrun]

19 minutes ago, Quetzalcoatl72 said:

I couldn't work out how to add lenses to Stellarium to see the field of view because it asks for aperture, that detail is never mentioned when looking at camera lenses...

That's because most camera lenses have an adjustable iris, so the aperture can be varied. Usually the maximum is quoted (and often the minimum too). The effective aperture is focal length/focal ratio. So, the abovementioned Samyang 135, f/2 lens has an effective aperture of 135/2=67.5mm...but only when it's "wide open". You can still calculate it for any desired setting with the formula above though.

Edited June 4, 2021 by wulfrun

[vlaiv]

4 hours ago, Quetzalcoatl72 said:

I couldn't work out how to add lenses to Stellarium to see the field of view because it asks for aperture, that detail is never mentioned when looking at camera lenses, looking at these details you've provided I worked out that the current lens I have my eye on has an aperture of 50mm and that's the Canon EF 70-200mm F/4 L IS USM, does that sound pretty sharp to you? Than lens combined with the asi533 has andromeda in the perfect frame. The lens also can be zoomed in and out if I were to get something larger in the field. Thoughts?

Not sure if I can help you much with sharpness of that lens. Best I can do is this:

https://www.lensrentals.com/blog/2018/08/mtf-tests-for-the-canon-70-200mm-f4-is-ii/

In particular MTF charts.

Look at green line.

It is 30 lpmm and it is already below 0.8 to start with and drops as you move towards edge of the frame (for ASI533 it will stay pretty much at 0.8 as it has 16mm diagonal if I'm not mistaken).

Compare that curve to this one:

That is the lens I have at max aperture setting of F/1.4. - It is at 0.7 for 30 lpmm

Here is what M31 looks like with that lens at F/2

In my book that is really not very nice image of M31 - look at those bloated stars. Maybe situation would be better if I stopped the lens to F/2.8 or F/4.

There is simply no comparison to what 80mm scope can do:

Yes, it won't fit whole M31 in single FOV - but it can easily do so in two panels and sharpness and detail simply can't be achieved with lens.

[Quetzalcoatl72]

2 hours ago, vlaiv said:

Here is what M31 looks like with that lens at F/2

The lens would be always used at f/4 not f/2 at that magnification though, no? I can't compare to those great pictures. The only 2 I have is one taken at 70mm and with the ed80, both only had several frames stacked, I assume that 70mm has bloated stars. As they looked great to me at the time, a time before guiding, precise polar alignment, smoother mount, and filters. Can't wait to improve upon these in the near future, still unsure about where to go from. I could do mosaics but I still desire a lens/small aperture scope for taking images of the moon, sun(solar eclipse) and nature as a whole.

Andromeda.TIF andromeda_80.TIF

Edited June 5, 2021 by Quetzalcoatl72

[vlaiv]

8 hours ago, Quetzalcoatl72 said:

The lens would be always used at f/4 not f/2 at that magnification though, no? I can't compare to those great pictures. The only 2 I have is one taken at 70mm and with the ed80, both only had several frames stacked, I assume that 70mm has bloated stars. As they looked great to me at the time, a time before guiding, precise polar alignment, smoother mount, and filters. Can't wait to improve upon these in the near future, still unsure about where to go from. I could do mosaics but I still desire a lens/small aperture scope for taking images of the moon, sun(solar eclipse) and nature as a whole.

Andromeda.TIF 103.14 MB · 0 downloads andromeda_80.TIF 103.14 MB · 0 downloads

Lens that you are interested in is F/4 lens so obviously can't be used at F/2. I just wanted to point out that MTF graphs suggest that lens that I used, at F/2 has similar performance to the one you are interested in - at F/4 and 200mm setting.

Then I just pointed out that you'll get much sharper image with a scope.  That's all I'm trying to say.

If you still want to use lens - by all means do.

The two images you attached are both nice, and nicely show the difference between good optics and one that is not as good when used on such target / in such a way.

Here, look:

I'd say that at this resolution - it is very nice image. At this resolution, you can no longer resolve issues that optic has - and therefore, it is good optics to work on that resolution.

Similar thing happens to lenses - they are fine for low resolution work - but not for high resolution work.

This is the same image - except presented at resolution it was shot at - you can clearly see that optics is not capable of resolving properly at this resolution.

Lens are like that - they can't properly resolve things at pixel size / sampling rate you are going to use them with.

Scopes on the other hand - can and will - your other image shows this:

It might be somewhat lacking in exposure time and processing - but these are things that can be improved upon with work - otherwise, image is sharp and stars are nice.

That was all I was trying to say - lenses have their issues when used for astrophotography. If you are aware of their limitations and work with them in proper way - they can produce nice results. However, they can't compete with scopes in some areas - they simply can't be as sharp.