Are any of these telescopes good for Astrophography?

[malc-c]

You could run an extension lead, but the issue is dampness and dew formation, which with 240v could lead to it tripping the house fuse board, or worse a potential shock when you come to unplug things, hence the suggestion to run low voltage 12v to the mount or use a battery.

Use the search function to research polar alignment... there are hundreds of posts on how to do it using  the polarscope built into the mount. - saves repeating what has already been written.  There are also old but excellent videos on youtube on using EQMOD to position the mount and align polaris in the bubble. 

And yes... you need deep pockets to get into imaging... but unlike other hobbies after the initial outlay you don't have to add further expense... unless you want to.

[AlanP_]

So here is what my setup might look like. Canon 600d, T2 adapter for canon camera,  Baader MPCC Mark III, Optolong L-Pro, and then my TS Photon 6". How do I know if my spacing is correct for the coma corrector with this setup?

[Davey-T]

5 minutes ago, AlanP_ said:

So here is what my setup might look like. Canon 600d, T2 adapter for canon camera,  Baader MPCC Mark III, Optolong L-Pro, and then my TS Photon 6". How do I know if my spacing is correct for the coma corrector with this setup?

Don't know but would think it comes as standard to fit Canon camera T ring and give correct back focus.

Dave

[AlanP_]

Just now, Davey-T said:

Don't know but would think it comes as standard to fit Canon camera T ring and give correct back focus.

Dave

Perfect, cheers Dave. What order does it come in with the 2" filter? Its not a clip in one.

[Davey-T]

Just now, AlanP_ said:

Perfect, cheers Dave. What order does it come in with the 2" filter? Its not a clip in one.

Something should have a 2" filter thread in it, maybe the front of the CC, if it's behind the CC then theoretically you need to add on a third of the filter thickness but best to try it as is first to see if it's necessary.

Dave

[AlanP_]

6 minutes ago, Davey-T said:

Something should have a 2" filter thread in it, maybe the front of the CC, if it's behind the CC then theoretically you need to add on a third of the filter thickness but best to try it as is first to see if it's necessary.

Dave

Contacted FLO and they said that the baader CC allows you to screw a filter into the nose so I think it will be ok.

[Waldemar]

1 hour ago, AlanP_ said:

So here is what my setup might look like. Canon 600d, T2 adapter for canon camera,  Baader MPCC Mark III, Optolong L-Pro, and then my TS Photon 6". How do I know if my spacing is correct for the coma corrector with this setup?

This is how you know you got the right spacing and which way to adjust:  FF distance to sensor.docx

[planetman83]

Hello guys,

I am thinking of buying the ts photon 6" f/5 in order to do astrophotography with my canon 6D (full frame). I don't want to autoguide. I think that 40-50sec frames will be enough with ISO6400. I want to ask:

1) Will a skywatcher eq5 Pro is capable of driving this setup?

2) I know that there will be coma. Is this coma corrector going to fix my field well enough ? https://www.teleskop-express.de/shop/product_info.php/info/p6706_TS-Optics-NEWTON-Coma-Corrector-1-0x-GPU-Superflat---4-element---2--connection.html Where can I see a photo sample with this setup and a full frame camera?

[vlaiv]

2 minutes ago, planetman83 said:

Hello guys,

I am thinking of buying the ts photon 6" f/5 in order to do astrophotography with my canon 6D (full frame). I don't want to autoguide. I think that 40-50sec frames will be enough with ISO6400. I want to ask:

1) Will a skywatcher eq5 Pro is capable of driving this setup?

2) I know that there will be coma. Is this coma corrector going to fix my field well enough ? https://www.teleskop-express.de/shop/product_info.php/info/p6706_TS-Optics-NEWTON-Coma-Corrector-1-0x-GPU-Superflat---4-element---2--connection.html Where can I see a photo sample with this setup and a full frame camera?

EQ5 will be able to hold it together and you'll be able to do 40-50s subs - however, not 100% of the them. You will likely need to discard some percentage of subs due to elongation. How much exactly - it is hard to say - depends on particular mount, but at least about 20% and even up to 50% of subs.

This will happen with even more expensive mounts - in fact any mount that does not have encoders. Periodic error correction will reduce number of discarded subs - but it won't eliminate problem completely.

Guiding is really best solution for that problem.

Full frame sensor will likely be wasted on scope like this - it simply can't illuminate 45mm diagonal. I think that you won't be able to correct that large circle. Something like 30mm is max diameter that will give satisfactory performance.

In fact - TS gives information on that, so you can judge for your self. Apparently this scope has large secondary (63mm - 42% CO - very uncommon for newtonians unless specifically designed to be astrographs) and still illuminates 38mm with 90% illumination. I suspect that corners of full frame will be less than 50% illuminated.

Nothing that flat can't fix - but SNR in corners will suffer because of this.

TSGPU coma corrector apparently also corrects up to 45mm - but I'm sort of skeptical of that claim - 2" coma corrector - that long is supposed to correct for almost complete 2" field? One thing is certain - it will vignette field even further.

In any case - they also recommend using APS-C format.

Very few scopes are capable of fully exploiting full frame sensor.

[planetman83]

Thank you very much for your help. So yes, the full frame sensor helps a lot with noise. So if I accept that I will crop and keep let's say the 60-70% of the length of the image, is going to be good enough then?

Edited January 22, 2021 by planetman83

[vlaiv]

2 minutes ago, planetman83 said:

Thank you very much for your help. So yes, the full frame sensor helps a lot with noise. So if I accept that I will crop and keep let's say the 60% of the length of the image, is going to be good enough then?

Full frame sensor helps with noise because of it's size / size of it's pixels. In any case - you can certainly try and you'll judge how much of field is usable to you - it might turn out that even larger portion of the field is usable on some targets.

[planetman83]

I could try IF I ALREADY HAD the setup. That's why I' m asking before buying. Anyway. What about the corrector? Which one will work best?

[vlaiv]

54 minutes ago, planetman83 said:

I could try IF I ALREADY HAD the setup. That's why I' m asking before buying. Anyway. What about the corrector? Which one will work best?

I wanted to say that if you are ready to loose some of the field - then just go ahead and get that setup - it might turn out that you loose much less then you anticipated (you mentioned using only 60% of field - maybe it turns out that you get 80-90% usable field).

As for coma corrector - well, I'm not the best person to answer that as I don't have any experience with CCs - but from what I've read online, I guess this one is fairly good:

https://www.teleskop-express.de/shop/product_info.php/info/p6706_TS-Optics-NEWTON-Coma-Corrector-1-0x-GPU-Superflat---4-element---2--connection.html

It also has spot diagram and spots do look fairly good even at 22mm from optical axis - which is effectively radius of full frame field (diagonal of 45mm = radius of 22.5mm).

You have this comparison:

https://www.astrofotoblog.eu/?p=856

but do keep in mind that it is using sensor that has less than 23mm diagonal - so only half of full frame (<25% usable area of FF sensor). Not sure what results will be further of axis for each of those CCs on test. Scope used is F/4 as well and you plan to use F/5 version.

 

[planetman83]

If I choose the f/4 over the f/5, the advantages are that with smaller focal length, most frames will be good, the frames will be brighter but the disadvantage is that the stars will be worse at the corners, right?

[alacant]

9 minutes ago, planetman83 said:

right?

Hi

No. f4 or f5, the brightness will be the same. The only way to get brighter frames would be to use a telescope with a larger aperture.

Cheers

**EDIT:  +1 with @vlaiv on choice of the GPU cc, Especially if you go with the f4. 

Edited January 22, 2021 by alacant

[vlaiv]

10 minutes ago, planetman83 said:

If I choose the f/4 over the f/5, the advantages are that with smaller focal length, most frames will be good, the frames will be brighter but the disadvantage is that the stars will be worse at the corners, right?

Change in focal length is not that big to make major impact on number of frames.

With Canon 6D and 6.55µm pixel size and 750mm of focal length, you will be working at 1.8"/px if you leave things as they are. With F/4 version you'll be working at 2.25"/px.

Usual P2P error of EQ5 class mount can easily be 30-40". It has 10 minute worm period or 600 seconds. This means that roughly in 300s it creates 30" long streak. If motion is uniform this means that 50s exposure will have 5" long trails - or about 2.5px regardless of focal length (too small difference in sampling rate). Periodic error is usually not that smooth and there will be jumps and slow parts - so you'll get sub with 5px smear and one with less than 1px smear - of course, you'll keep all those that have less than 1-2px of smear and discard ones with longer smear. In any case - there will be not much of difference there between F/4 and F/5.

You could say that you can image for shorter time at F/4 vs F/5 but your sub duration should be dictated by amount of read noise and how it relates to other noise sources rather than speed of your scope. Nothing preventing you to go with 30s subs if that keeps you larger percent of the subs - and I would advocate that strategy as loss from read noise issues is likely to be overcome by increased total imaging time (percentage of kept subs).

However, F/4 is hard to work with - collimation is very sensitive, requires better coma corrector - all things that might go wrong like tilt and such will produce greater errors than at F/5 - and I would recommend such fast scope only to people having experience with slower newtonians - and not someone who is just switching to this type of scope for imaging.

14 minutes ago, alacant said:

Hi

No. f4 or f5, the brightness will be the same. The only way to get brighter frames would be to use a telescope with a larger aperture.

Cheers

If you keep camera the same, then yes, F/4 will be brighter than F/5 for same exposure time. This is because of same aperture capturing light - but more of that light is summed onto a single pixel - and we read off value per pixel. Light per pixel will increase so will signal strength per pixel and image will be brighter.

[planetman83]

The truth is that I am not new to imaging. I have changed many setup the last 13 years. I observe using a 16" f/4.5. I collimate with the tublug and 2" laser tools, so collimation will not be a problem. I know that the f/4 's length is smaller and the focal length is smaller so more frames will be good compared to f/5. The biggest problem for me is how well the corrector will work on f/4 compared to f/5.

[vlaiv]

2 minutes ago, planetman83 said:

The truth is that I am not new to imaging. I have changed many setup the last 13 years. I observe using a 16" f/4.5. I collimate with the tublug and 2" laser tools, so collimation will not be a problem. I know that the f/4 's length is smaller and the focal length is smaller so more frames will be good compared to f/5. The biggest problem for me is how well the corrector will work on f/4 compared to f/5.

Well, you have spot diagram for TSGPU CC that was made with F/4 scope. That should be very good indicator of it's performance at F/4

[planetman83]

3 minutes ago, vlaiv said:

Well, you have spot diagram for TSGPU CC that was made with F/4 scope. That should be very good indicator of it's performance at F/4

This is something I don't know how to read and understand. First time I hear about it. What is your outcome?

[alacant]

52 minutes ago, vlaiv said:

Light per pixel will increase

Not sure. Take a shot of m38 with both. Make them the same size on the screen. The same; neither darker nor brighter. Maybe you mean it seems brighter because it's smaller?

 

18 minutes ago, planetman83 said:

First time I hear about it.

Hands on tells us that with our 208mm f3.9, the GPU beats the Baader and the gso by a noticeable margin.

Cheers

[vlaiv]

1 minute ago, planetman83 said:

This is something I don't know how to read and understand. First time I hear about it. What is your outcome?

Reference circle in this case is 100µm. Unfortunately it does not say which scope is this for, but let's assume it is for 8" F/4 newtonian. IMA number is distance from optical axis - this diagram covers FF sensor as it provides spot diagram up to 22mm away from optical axis.

8" F/4 newtonian has 5µm airy disk diameter. For diffraction limited system - spot diagram should end up inside this 5µm disk.

We can clearly see that if above spot diagram is for 8" F/4 newtoninan - system is not diffraction limited as GEO radius for each field is twice as wide (Radius for most distances from optical axis is bigger tham 5µm). But we are not talking about planetary imaging - we are talking about DSO imaging with long exposure and untracked one.

You have camera with 6.55µm pixel size - this means that stars in center and at the edge of the frame will be no more than 2px wide (this is without influence of atmosphere and mount tracking errors). That is good enough for your intended working resolution.

Things might be a bit worse at 6" model, but still - that is good enough across whole field. Mind you - this is best case scenario where distance between sensor and coma corrector has been set to optimum and mirror has perfect shape, there is not tilt in the system. In another words - this CC has potential to perform very well indeed, but in reality it is up to all these things that add up if performance will be good.

Mind you, that test that I've linked - has F/4 10" scope with very good focuser, very good mount, and yet, 11mm away from optical axis, stars look like this:

That is with 5.4µm pixel size of Kaf8300. To my eye - these stars look bloated and maybe a bit out of focus as well (field curvature?). I would not expect that 11mm away from optical axis for well corrected system.

Granted, it might have been very poor seeing on that particular night?

 

[vlaiv]

1 minute ago, alacant said:

Not sure. Take a shot of m38 with both. Make them the same size on the screen. The same; neither darker nor brighter. Maybe you mean it seems brighter because it's smaller?

No, it will not seem brighter - actual pixel values will be higher and if you prepare images in the same way (scale histogram to same values, apply same stretch, etc ...) it will be actually brighter.

There are two things that determine how bright image is - or let's use term that is less ambiguous - how big ADU values in pixels are.

First is aperture size.

Second is working resolution in terms of arc seconds per pixel.

Larger aperture means more light collected

Lower working resolution means that same light is divided between less pixels - so each pixel gets more of the total captured light.

This holds for extended sources - point sources like stars behave differently and there resolution also plays a part but we have to examine stellar profile which is "bell shaped" so not every pixel gets more or less equal amount of light.

In changing focal length and keeping aperture the same - we keep amount of light / number of photons gathered the same - but distribute it over fewer pixels - which in turn means that each pixel will get larger number of photons and have larger ADU value as a result.

[alacant]

24 minutes ago, vlaiv said:

each pixel will get larger number of photons

Mmm. Same aperture, same camera, same number of pixels, same number of photons... From where do the extra photons come?

Confused!

[vlaiv]

1 minute ago, alacant said:

Mmm. Same aperture, same camera, same number of pixels, same number of photons... From where do the extra photons come?

Confused!

Different focal length - different amount of sky covered by single pixel

Say there is nebula that is perfect square and has 4" x 4" in dimensions. It emits 16 photons each second that falls on telescope aperture.

If you have such focal length that 4" x 4" of the sky is mapped on 4px x 4px - 16 px total (resolution of 1"/px), then those 16 photons each second end up divided by 16 pixels. Each pixel gets 1 photon per second. Integrate for 1 minute and each pixel gets 60 photons (let's have QE of 100% and gain of 1e/ADU) - or 60 ADU.

Now instead, use same nebula, same aperture - we still get 16 photons per second from that nebula, amount of photons has not changed, but half the focal length of telescope.

We now have 2px x 2px covering the nebula - or total of 4px (resolution of 2"/px). Now 16 photons each second is divided among 4 px (not 16px as above). This means that each pixel gets 4 photons per second, or if we integrate for 1 minute, each pixel will now have 240 ADU instead of 60 ADU - image is brighter.

Note that we don't have to also change pixel size for this to happen - nor we have to change focal length when we change pixel size for this to happen - it happens when we change either of the two (or both). It happens any time sampling resolution has changed.

This is why only two things are important - aperture size - which determines how much photons is captured and working resolution - which determines into how many "parts" those captured photons are divided.

This is also the reason why you can improve SNR by binning even after capture (software binning) - by taking divided signal and putting it back together.

[alacant]

27 minutes ago, vlaiv said:

aperture size

So the illusion that f4 is brighter than f5 actually isn't an illusion at all. F4 is brighter than f5. Nice:)

Cheers