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a couple of questions about astrophotography

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#1 Ring_Singularity

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Posted 27 February 2021 - 02:12 AM

I'm doing untracked astrophotography using the 500 rule (seems to work well)......75mm (150mm EFL), comes out to 3.2 seconds per subframe. However I want to do longer exposures without stars streaking. The Sequator software I use offers an option to do 2x2 binning (reducing the resolution from 16 MP to 4 MP). It occurs to me this would also allow me to do 2x longer exposures without star trails since the resolution would be reduced by 2x across each dimension. My question is- is it worth it? Would reducing the resolution like this allow me to capture twice as many stars since I was doubling the shutter speed? If so, I could go even further and create files that were 4x4 binned (going from 16 MP to 1 MP or screen size) and thus make the shutter speed 4x longer or 13 seconds.....would this mean I would capture 4x as many stars? What is the tradeoff?

 

^that's for untracked photography on a conventional tripod.

 

Now, since I have the 8 SE  I have its mount and I expect that even on this alt az mount I should be able to do a lot better with my camera OMD EM10 II and 75-300 lens?  At 75mm how long of an exposure should I be able to do on this mount to get the equivalent of the 500 rule on a conventional tripod?  At 300mm?  How would I go about mounting this camera on it?  Thanks!

 



#2 deansjc

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Posted 27 February 2021 - 08:59 AM

There is an app available called Pin Point Stars that might assist here.  It is available for Android, perhaps IOS and claims to improve on the "outdated" rues of 500 and 600.

 

John


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#3 B 26354

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Posted 27 February 2021 - 11:03 AM

...since I have the 8 SE  I have its mount and I expect that even on this alt az mount I should be able to do a lot better with my camera OMD EM10 II and 75-300 lens?  At 75mm how long of an exposure should I be able to do on this mount to get the equivalent of the 500 rule on a conventional tripod?  At 300mm?  How would I go about mounting this camera on it?  Thanks!

Use this, to piggyback your camera on the 8SE:

 

https://www.amazon.c...9/dp/B003VL8D2M

 

   ---

 

I'm not at all familiar with the 8SE mount, but I assume that it's capable of tracking, for visual use.... which means that you "should" be able to take somewhat longer exposures without getting any trailing, than you would on a static mount.

 

But since you're using an alt-az mount... over a period of time, you'll still get field rotation, for which some types of stacking software can compensate... but only to a limited degree.

 

And rather than relying on an "app" to figure out what your longest un-trailed exposure can be at a given focal-length... why not just take a few bracketed exposures, and see for yourself? That way, you'll know for sure.  waytogo.gif  grin.gif


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#4 Ring_Singularity

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Posted 28 February 2021 - 04:30 AM

Use this, to piggyback your camera on the 8SE:

 

https://www.amazon.c...9/dp/B003VL8D2M

 

   ---

 

I'm not at all familiar with the 8SE mount, but I assume that it's capable of tracking, for visual use.... which means that you "should" be able to take somewhat longer exposures without getting any trailing, than you would on a static mount.

 

But since you're using an alt-az mount... over a period of time, you'll still get field rotation, for which some types of stacking software can compensate... but only to a limited degree.

 

And rather than relying on an "app" to figure out what your longest un-trailed exposure can be at a given focal-length... why not just take a few bracketed exposures, and see for yourself? That way, you'll know for sure.  waytogo.gif  grin.gif

Thanks this is really appreciated!  So the camera would piggy back on the scope?  Well people have told me the mount is good for at least 30 sec exposures at reasonable focal lengths, and that would be good enough for me to stack a bunch of them.

 

I really want to get this item you linked me to and Amazon says I should get two additional things with it, would those be of use for me since I have an Olympus camera?

 

https://www.amazon.c...9/dp/B003VL8D2M

 

Buy the selected items together

This item:Celestron Universal Piggyback Mount $30.34

Celestron 93419 T-Ring for 35 mm Canon EOS Camera (Black) $13.89

Celestron T-Adapter with SCT 5, 6, 8 with 9.25, 11, 14, Black (93633-A) $27.34

 

I suspect the T-Adapter would work with my camera for attaching and using the scope as the lens, but what about this T-Ring?  Does that only work for Canon cameras and do I need something else for my camera?


Edited by Ring_Singularity, 28 February 2021 - 04:30 AM.


#5 Maritime

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Posted 28 February 2021 - 03:24 PM

Investigate flip mirror diagonals as well. 



#6 charlesgeiger

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Posted 01 March 2021 - 02:04 AM

All you need is the bracket which mounts on your C8.  That will allow you to mount your camera and lens piggyback onto the scope.  If you want to get the longest exposures you can, you would need to get a wedge and have your C8 equatorially mounted and polar aligned.  Your alt/az configuration will let you take short exposures that you can stack but as mentioned, field rotation will occur after a minute or so (you will have to determine by taking exposures bracketed).

That other stuff to go along with your bracket is just for mounting your camera without its lens to the telescope to use the telescope as the lens and your camera body to take the exposures.  You are then talking about a 2,000mm focal length as opposed to your own camera with its 75 to 300mm focal length.  The extra long focal length (2,000mm) would require extremely short exposures of maybe 2-3 seconds at best before you get trailing.  And you would be shooting at f/10.  So, if I understand correctly, you want to use your camera at its 75-300mm focal length, would be the way you would start using the piggyback configuration.

Charlie


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#7 Ring_Singularity

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Posted 01 March 2021 - 05:45 AM

All you need is the bracket which mounts on your C8.  That will allow you to mount your camera and lens piggyback onto the scope.  If you want to get the longest exposures you can, you would need to get a wedge and have your C8 equatorially mounted and polar aligned.  Your alt/az configuration will let you take short exposures that you can stack but as mentioned, field rotation will occur after a minute or so (you will have to determine by taking exposures bracketed).

That other stuff to go along with your bracket is just for mounting your camera without its lens to the telescope to use the telescope as the lens and your camera body to take the exposures.  You are then talking about a 2,000mm focal length as opposed to your own camera with its 75 to 300mm focal length.  The extra long focal length (2,000mm) would require extremely short exposures of maybe 2-3 seconds at best before you get trailing.  And you would be shooting at f/10.  So, if I understand correctly, you want to use your camera at its 75-300mm focal length, would be the way you would start using the piggyback configuration.

Charlie

Thanks this is exactly what I wanted.  In addition to that though I also have the f/6.3 Celestron corrector/reducer, so at 1280mm f/6.3 would that make astrophotography significantly easier on this SE mount or still only give me less than 10 seconds per subframe?  I only get 3.2 seconds per subframe right now with my 75-300 lens at 75mm or full wide (150mm EFL) using the 500 rule on just a regular lightweight tripod.  What should I be able to get at the same focal length with this piggyback set up?  And at 300mm (full tele)?  Thanks!



#8 Ring_Singularity

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Posted 01 March 2021 - 08:32 AM

I also found this thread, should I get one of these other things instead?

 

https://www.cloudyni...-dslr-question/

 

 

http://www.scopestuff.com/ss_sbcm.htm

 

http://www.celestron...piggyback-mount

 

http://www.highpoint...Dg4kaAg6s8P8HAQ

 

http://www.telescope...c/38/p/7388.uts

 

note:  I dont like "heavy" cameras- any camera+lens combo I will use will weigh 1 kg or less.  The OMD EM10 Mk II with the 75-300mm lens combo together weigh less than 900g.  Anything else I'd be likely to use would also have to weigh less than 1 kg.

 

Also the last question in that thread went unanswered.

 

How about attaching your camera and lens to a dovetail and putting them on the mount in place of the SCT? Less weight on the mount will improve tracking.


Edited by Ring_Singularity, 01 March 2021 - 09:09 AM.


#9 Ring_Singularity

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Posted 01 March 2021 - 09:08 AM

https://www.cloudyni...-exposure-time/

 

https://www.cloudyni...with-8se-mount/

 

Based on this, it seems I need to avoid 30 sec exposure times because of field rotation and periodic error correction regardless of whatever lens I use?  Sounds like I should cap my shutter speeds to around 20mm regardless of the lens focal length?

 

https://www.cloudyni...g-and-stacking/

 

https://www.cloudyni...eight-overkill/

 

Also found this JMI version is this better or about equal to the Celestron version?

 

https://www.bhphotov...et_for_the.html

 

https://www.bhphotov...e.html/overview

 

They both reference 7 min as the maximum exposure time (I assume this is with a wide angle lens, I would never go over 1 minute timed exposures and would be using 75-300mm focal lengths.)

 

https://www.bhphotov...he.html/reviews



#10 charlesgeiger

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Posted 01 March 2021 - 02:18 PM

The 1280mm f/6.3 reducer corrector will make it easier to get subs with using the telescope as camera.  But you are still at 1280mm.  You would need to experiment.  I would say you might get 10 to 15 second exposures using the alt/az mount.  You might get 1 to 3 minutes with the wedge polar aligned.  A lot depends on your drive accuracy and your polar alignment.  You might get longer single exposures if you use a dedicated auto tracker.  

If you want to get your camera with its 75-300mm lens to do the astrophotography, you will need a hard connection to your scope.  The Celestron bracket or something similar generic will do the trick.  If you need to be concerned with balance of your scope with any of the additional equipment you may add, you may want a dovetail rail with an adjustable connector for camera or for a sliding counterweight.  I would start with just the hard connection (camera to telescope) and see how things proceed.

Charlie



#11 Ring_Singularity

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Posted 03 March 2021 - 05:16 AM

The 1280mm f/6.3 reducer corrector will make it easier to get subs with using the telescope as camera.  But you are still at 1280mm.  You would need to experiment.  I would say you might get 10 to 15 second exposures using the alt/az mount.  You might get 1 to 3 minutes with the wedge polar aligned.  A lot depends on your drive accuracy and your polar alignment.  You might get longer single exposures if you use a dedicated auto tracker.  

If you want to get your camera with its 75-300mm lens to do the astrophotography, you will need a hard connection to your scope.  The Celestron bracket or something similar generic will do the trick.  If you need to be concerned with balance of your scope with any of the additional equipment you may add, you may want a dovetail rail with an adjustable connector for camera or for a sliding counterweight.  I would start with just the hard connection (camera to telescope) and see how things proceed.

Charlie

Thanks- at what focal length do you think I could get 1 minute subs?  300mm on my 75-300mm lens?  Also, is there any way to get the camera on the mount without the telescope and do alignment with the camera itself?  Or to do alignment with the telescope, then remove it, and put the camera on the dovetail?

 

The camera+lens combo is fairly lightweight, less than 1 kg (around 850g), so it shouldn't need any counterweights or have any balancing issues?  Does a dovetail with an adjustable connector for the camera allow me to use the camera without the scope on the mount?


Edited by Ring_Singularity, 03 March 2021 - 05:34 AM.


#12 starstruck85

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Posted 03 March 2021 - 08:43 AM

Does a dovetail with an adjustable connector for the camera allow me to use the camera without the scope on the mount?

Hi Ring,

 

I think if you want to just use the camera with the mount and skip the SCT, you would need a "L" bracket like this: https://www.amazon.c...e/dp/B001DGR54O

 

At first, it seems like it wouldn't work, because you have to move your SE mount's dovetail saddle to a vertical position to place the "L" bracket in the saddle. Surprisingly, you can still align and track normally like this (disclaimer: I've only tried this with a small scope and the SLT mount, but I think it would be the same for a camera and the SE mount).

 

Here are some other ideas: https://www.cloudyni...-on-nextar-arm/


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#13 Ring_Singularity

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Posted 03 March 2021 - 09:01 AM

Hi Ring,

 

I think if you want to just use the camera with the mount and skip the SCT, you would need a "L" bracket like this: https://www.amazon.c...e/dp/B001DGR54O

 

At first, it seems like it wouldn't work, because you have to move your SE mount's dovetail saddle to a vertical position to place the "L" bracket in the saddle. Surprisingly, you can still align and track normally like this (disclaimer: I've only tried this with a small scope and the SLT mount, but I think it would be the same for a camera and the SE mount).

 

Here are some other ideas: https://www.cloudyni...-on-nextar-arm/

wow this is interesting!  I wouldn't need to get the piggy back adapter if I got this?



#14 Ring_Singularity

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Posted 03 March 2021 - 09:09 AM

Which would let me take longer exposures, the piggyback adapter or the L adapter above? I saw a 1 min exposure of M42 Orion nebula with a 300mm Sigma lens on the Nexstar mount at the above link!


Edited by Ring_Singularity, 03 March 2021 - 09:10 AM.


#15 starstruck85

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Posted 03 March 2021 - 04:52 PM

wow this is interesting!  I wouldn't need to get the piggy back adapter if I got this?

That's right. You'd be attaching the camera direct to the mount. I think it would be preferable to find one that attaches horizontally, but I'm not sure there is one commercially made. It may need to be DIY in that case.

 

I'd imagine not having the heavy SCT mounted should improve things for wide field shots, but I really cannot speak from experience on it.


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#16 Ring_Singularity

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Posted 05 March 2021 - 12:35 AM

That's right. You'd be attaching the camera direct to the mount. I think it would be preferable to find one that attaches horizontally, but I'm not sure there is one commercially made. It may need to be DIY in that case.

 

I'd imagine not having the heavy SCT mounted should improve things for wide field shots, but I really cannot speak from experience on it.

Yes I think I will just get them both and then decide which one works better for me.  One is 30 and the other is 34 so getting one of each seems pretty cost efficient and this way I have the opportunity to try different set ups.

 

My only question is would I be able to do an alignment just using the camera lens.....basically the only star I can clearly see in the camera LCD is Sirius lol.  I guess I could do a solar system align, but I dont know how accurate that is (good enough for 1 minute exposures at 300mm?)


Edited by Ring_Singularity, 05 March 2021 - 12:35 AM.


#17 starstruck85

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Posted 05 March 2021 - 04:19 PM

I believe the 1 minute exposure that was referred to in the link I posted was a SE mount with a wedge. That's a whole different ballgame. From my limited experience, I don't think you'll approach that in alt az... however you should be able to take shorter exposures that you can then run through stacking/alignment software for decent results.

 

I'm by no means an expert, so take it all with a grain of salt. You also might want to see what kind of responses you can get in the DSLR sub forum in regards to exposure lengths in alt az.


Edited by starstruck85, 05 March 2021 - 04:25 PM.

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#18 ayadai

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Posted 06 March 2021 - 03:14 AM

I've gotten decent 15-second exposures with my 8SE and D5500. The main issue with this mount and OTA for me is wind. Anything over 3-4 knots will create sufficient shake to bork an image.


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#19 Ring_Singularity

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Posted 06 March 2021 - 04:26 AM

I believe the 1 minute exposure that was referred to in the link I posted was a SE mount with a wedge. That's a whole different ballgame. From my limited experience, I don't think you'll approach that in alt az... however you should be able to take shorter exposures that you can then run through stacking/alignment software for decent results.

 

I'm by no means an expert, so take it all with a grain of salt. You also might want to see what kind of responses you can get in the DSLR sub forum in regards to exposure lengths in alt az.

It sounds a lot better than what I get right now with my static tripod and using the 500 rule



#20 Ring_Singularity

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Posted 06 March 2021 - 04:27 AM

I've gotten decent 15-second exposures with my 8SE and D5500. The main issue with this mount and OTA for me is wind. Anything over 3-4 knots will create sufficient shake to bork an image.

Thanks, whats the focal length of the lens you are using with the camera?  Are you beating the 500 rule (using 35mm format equivalent focal lengths?)  Did you get the piggyback adapter or the L bracket or both?  I have the Celestron Vibration Suppression Pads so that should be a big help.  I just need to know if piggybacking a 1 kg camera on this mount with the 8" OTA is okay or should I go for the L bracket and only mount the camera?


Edited by Ring_Singularity, 06 March 2021 - 04:30 AM.


#21 Ring_Singularity

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Posted 06 March 2021 - 04:47 AM

That's right. You'd be attaching the camera direct to the mount. I think it would be preferable to find one that attaches horizontally, but I'm not sure there is one commercially made. It may need to be DIY in that case.

 

I'd imagine not having the heavy SCT mounted should improve things for wide field shots, but I really cannot speak from experience on it.

There's a specific name for the type of dovetail on the SE mount, right?  CG-5 I think it's called?  I've been looking for a "CG-5 dovetail to 1/4 inch adapter"  so far no results.

 

edit- hold on, what about this, would this work on the SE mount and is it better than that L adapter thing that needs to be mounted vertically?

 

https://www.amazon.c...5024197&sr=8-19


Edited by Ring_Singularity, 06 March 2021 - 04:52 AM.


#22 ayadai

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Posted 06 March 2021 - 04:01 PM

Thanks, whats the focal length of the lens you are using with the camera?  Are you beating the 500 rule (using 35mm format equivalent focal lengths?)  Did you get the piggyback adapter or the L bracket or both?  I have the Celestron Vibration Suppression Pads so that should be a big help.  I just need to know if piggybacking a 1 kg camera on this mount with the 8" OTA is okay or should I go for the L bracket and only mount the camera?

I'm actually using a t-adapter and t-ring to connect the DLSR directly to the OTA.



#23 Ring_Singularity

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Posted 07 March 2021 - 11:45 PM

https://www.amazon.c...5024197&sr=8-19

 

would this thing work or not on the SE mount because the dovetail is on the side and the camera on this kind of platform would actually be vertically oriented (portrait mode) not horizontally (landscape mode)?

 

I'm also thinking that L adapter linked to earlier would be good for me to use my Celestron Skymaster 15x70 and 20x80 binos with?  I could even align the mount with them and track!



#24 ayadai

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Posted 07 March 2021 - 11:54 PM

https://www.amazon.c...5024197&sr=8-19

 

would this thing work or not on the SE mount because the dovetail is on the side and the camera on this kind of platform would actually be vertically oriented (portrait mode) not horizontally (landscape mode)?

 

I'm also thinking that L adapter linked to earlier would be good for me to use my Celestron Skymaster 15x70 and 20x80 binos with?  I could even align the mount with them and track!

The adapter would put it in "portrait" orientation. If you wish to have "landscape" orientation of objects in your camera's viewfinder, you'll need the L adapter. The same holds true with binoculars, although I think that a simple tripod would be better for them, as you'll have less latitude for adjustments for comfort on the telescope mount, which is the ostensible reason for mounting binoculars.


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#25 Ring_Singularity

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Posted 08 March 2021 - 12:03 AM

The adapter would put it in "portrait" orientation. If you wish to have "landscape" orientation of objects in your camera's viewfinder, you'll need the L adapter. The same holds true with binoculars, although I think that a simple tripod would be better for them, as you'll have less latitude for adjustments for comfort on the telescope mount, which is the ostensible reason for mounting binoculars.

You're right....I think I'll go with the piggyback adapter for when I want the camera+lens riding atop the scope and the L adapter for when I want to use the camera+lens or the binoculars without the scope.  Dont think I should be using the piggyback adapter for the binos anyway since one weighs 3 pounds and the other one weighs 6 pounds lol, that's probably too much for the SE mount with the 8" SCT OTA on it already.

 

So with the piggyback adapter and the L adapter I should be all set for what I want to do either with or without the OTA on the SE mount?

 

I can move the binos on that mount up/down on the dovetail to adjust them for comfortable viewing, correct?  I have a normal heavy duty tripod but I'd have to bend down to be able to see through the binos if I use that (the tripod is max 70" tall and I'm 5ft 6in.)

 

https://www.bestbuy....wE&gclsrc=aw.ds

 

This is my regular tripod that I use

 

70" 2 in 1 Tripod and Monopod

 

Maximum Weight Capacity 15.4 pounds

 

Maximum Extended Height  70 inches

 

Minimum Extended Height  21.5 inches

 

has bubble level


Edited by Ring_Singularity, 08 March 2021 - 12:09 AM.



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