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Steve91

Imaging with a DSLR

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Hi guys,

First ever night out with my scope on Thursday, tried taking a few pics of M42 using my DSLR. (Celestron 127 SLT and a Nikon D3100)

I encountered quite a few problems and hoped you guys would be able to help me out :) First things first i centered the target in a 25mm eyepiece, then switched from my eyepiece to my DSLR. I then had absolutely no idea if it was on target because the live view isn't sensitive enough to pick much up. So I decided to go to Jupiter to focus as its one of the few things my live seems to be able to pick up.

After that I slewed back to M42 and took an exposure of about 20 secs at 1600 iso, but nothing. So I spent ages taking pictures of random bits of sky until I eventually got M42 in the frame, it took me around 20 mins to find it.

So i'm wondering if having my DSLR on the back of my scope is affecting the goto's because of the added weight? Or am I doing the process completely out of order :o? Even with the 20 seconds exposure I was getting slight trails on the stars and sometimes I would just get a completely blurred image. I understand this isn't the perfect set up for astro but I was finding it incredibly difficult to even get a picture of anything.

Here and the results, sorry about the massive picture. I know there's alot of noise but that's down to a fairly high ISO and me taking darks at completely the wrong ISO (by mistake) Any advice would be much appreciated :)

T03ZUc1.jpg

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Even though it's a tracking mount your using here i would imagine the tripod and mount must be properly balanced,leveled and finally polar aligned to get properly accurate gotos.The handcontroller must be set up proper as well right? Does it require you put in your proper hemisphere,date and time and if it's daylight savings or not? Location in Longitude and Latitude? That has to be right on. Make sure the battery in the handset is good if it has one.Some do and when you turn off the mount it loses all the info.Your very close to some great pictures here. Just a bit of tweeking. Keep at it!

Edited by Leveye
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It is only an Alt-Az mount so I don't think it needs to be polar aligned. I did input the latitude and longitude. There's a little bubble thing on one of the legs and I always point that north and make sure it's dead level.

I tried taking the images after an hour or so of observing so i'm wondering if the tracking had gone out slightly over the period of an hour but not sure. Is it usually hard to locate what you want?

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Here's another one I got, not sure if its better or not. I've been following various guides on the internet to help me with DSS so I don't necessarily understand what i'm doing with the processing i'm just trusting the guides i'm following :p

xkxzCLH.jpg

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For the length of exposure here i'd say that's pretty good tracking. Your focus looks to be slightly off to me. If you can zoom in using liveview on a bright star and focus very very carefully.

Edited by Leveye

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I was finding it really hard to focus tbh, like I said I went for Jupiter as my live view can see that clearly and I did what I could. These images are about 10 shots at 10 seconds and around 1600 ISO I believe.

DSS did an amazing job of aligning them because the target started at the bottom of the frame and was at the top by the last shot.

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for focussing, make yourself a bahtinov mask - there's a site somewhere on the web that will calculate the correct template for one based on your aperture and focal length, then I made mine with some stiff card and a stanley knife.  Put that over the end of the scope, point at a bright nearby star (needs to be a point source, not Jupiter), and start taking test pics, you can inspect the pic on the camera screen, try to get all three diffraction spikes on the pic to go through the centre of the star and then you'll have focus, so you may need to repeat a few times till you're spot on.  Takes a bit of practice at first, but you'll get the hang of it,  Then you slew to your real target (and don't forget to take the mask off !).

Having a dslr on the scope shouldn't affect your goto, I do it like that all the time (though mine is an eq mount).  Your hand controller should have a feature allowing you to tell the synscan computer enhanced accuracy - on mine, when I'm centered on the target i hold down 'esc' for a couple of seconds, it asks me if I want to recenter for current object, and i select yes.  So with your eyepiece, aim at the target, recenter, slew to the star you'll be using to focus, recenter on that too.  The synscan computer should then have an accurate fix on both the target and the focus star, test it by seeing if it slews straight back to the target in one go.  Then bung in the dslr and you should be good to go.

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Do you have a link to the site for bahtinov mask? that sounds like a great idea, I've seen them before but thought they seemed expensive and wasn't quite sure how effective they were. I've got plenty of good card to make one out of.

I'll have a look on my handset tonight, or manual to see if I have that option.

Thanks for a great reply :)

Sent from my HTC One S using Tapatalk

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Thanks for the link :)

I obviously know the focal length and aperture of my scope but I don't really understand the "edge thickness" setting? Also I can't actually get to my scope right this second so can't do any measurements etc, any advice on that one?

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Plenty of Bat masks on Ebay! Good qualityt too!

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There's one on ebay which would suit my scope but it's still around £20 posted, if I can make one (like i did my dew shield for £3) I would be quite happy :p

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think the edge thickness is just the extra diameter of the mask  over the diameter of the telescope tube - I'd go for plenty, you can always trim it later.  My bahtinov mask looks very similar to my solar mask that I posted a pic of in this thread - http://stargazerslounge.com/topic/211141-solar-imaging-get-started/ and works a treat.

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When you say plenty am I looking at around 20mm?

Sent from my HTC One S using Tapatalk

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So i'm wondering if having my DSLR on the back of my scope is affecting the goto's because of the added weight? 

When you balance your scope you need to do it with everything set up as you are going to use it. So if you are going to use a camera, you need to balance the scope with the camera attached (and roughly focussed). As an example, I have just acquired and ED80, which is really easy to balance with an eye piece in it, however when I attach my DSLR with extra battery pack to the focuser it makes it really camera end heavy. So much so that even with the tube all the way to the end of the tube rings, and the dovetail all the way to the end it still needs a weight added to the other end in order to make it balance properly.

If you do not balance it, the GoTo will not be as accurate and you will put a lot more strain on the motors and gears. 

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Hi

I have read through this thread with interest. I am using a Celestron CPC800, so a similar mount to yours. I always use a bahtinov mask for focusing and a Canon 550d with Backyard EOS. I cannot comment on the Nikon as I have no knowledge of it but I can say that the Celestron mounts are very good if aligned properly. You can always get more accurate GOTO if you use the Precise GOTO function of the system which will ask you to centre on a star before goingto the target selected. I have had good results with this set up (see attached). Balance can be an issue and would also suggest the use of a light pollution filter and taking lots of exposures to stack and process. Just stick at it and I'm sure that you will be able to get some good results.

Peter

post-35423-0-22860800-1394972491_thumb.j

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I printed a bahtinov Mask, glued it to thick cardboard and cut it out, works perfect.

For M42 I would use Sirius for focusing, then its only a short movement to M42

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Hi

I have read through this thread with interest. I am using a Celestron CPC800, so a similar mount to yours. I always use a bahtinov mask for focusing and a Canon 550d with Backyard EOS. I cannot comment on the Nikon as I have no knowledge of it but I can say that the Celestron mounts are very good if aligned properly. You can always get more accurate GOTO if you use the Precise GOTO function of the system which will ask you to centre on a star before goingto the target selected. I have had good results with this set up (see attached). Balance can be an issue and would also suggest the use of a light pollution filter and taking lots of exposures to stack and process. Just stick at it and I'm sure that you will be able to get some good results.

Peter

That's an impressive picture :) I've not actually tried the precise goto yet, provably something I should check out.

I understand that it's best to set up with the balance as I'm going to be using but how can I balance the scope for my dslr and align at the same time?

And definitely looking into making a bahtinov, just need to make sure I do it accurately

Sent from my HTC One S using Tapatalk

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Hi Steve, you balance your scope before doing the alignment. I usually do it pretty early on in the setup, and a test one even before Polar Alignment.  

Your images are okay and normally about where most people start, as it's a very steep learning curve. Try using ISO 800 and keeping your images to about 30 secs - that way you will find your images should have less movement showing (blur). Once you have mastered tracking you will be able to take longer images.

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I don't actually bother to balance until I have got alignment. The reason is that I use an illuminated reticule eyepiece to get the most accurate alignment of the stars in the centre of the eyepiece. Once aligned I then attach the camera. I have worked out what it takes to balance the scope with various attachments so it is no problem to add weights depending on what you have on the scope. No Polar alignment required on an AltAz mount of course.

This works fine for me and the GOTO then works fine after the camera is added and, like I say, I usually use the Precise GOTO to save any misalignment issues. If you don't use Precise GOTO you can always take a capture to see where your target appears on the screen and you can adjust with the telescope motion controls.

Peter

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Hi Steve, you balance your scope before doing the alignment. I usually do it pretty early on in the setup, and a test one even before Polar Alignment.

Your images are okay and normally about where most people start, as it's a very steep learning curve. Try using ISO 800 and keeping your images to about 30 secs - that way you will find your images should have less movement showing (blur). Once you have mastered tracking you will be able to take longer images.

Thanks for the advice, as I only have an alt-az mount how would I balance it to match what it would be like with my dslr on?

Sent from my HTC One S using Tapatalk

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Hi Steve,

I started out attempting to image with an alt-az mount. It is possible to get some pictures of brighter nebulae and even some galaxies.

You will ofc be limited to the tracking capability of the mount. Adding in the factor that you will observe rotation along with longer exposures, this does mean you are really up against it.

That said its not impossible to get some nice images, its just a lot more effort! If I were to attempt imaging on this type of mount again I would avoid trying to go for the longest exposure I could possibly achieve. Although it seem to make sense to max your exposure times to get the most (which to be fair was my thinking too!) it really doesn't pay off enough to make for all the time you spend trying to get them and then returning to the pc later that night only to find your tracking is much worse than it at first appears.

20 seconds isnt really bad going, I think the maximum I ever achieved was 90 seconds but I am talking the exception rather than the rule.

My method was actually to get the mount fairly close to polar aligned (as close as I could get it anyway). It is probably correct to say that this is not imperative with alt-azimuth mounts but it does save a lot of time slewing about when you try to get your goto aligned. The most important factor I found was making sure the mount is level, this made the biggest noticeable difference to my tracking, second most important is the position in the sky of my target as geometry starts to take effect.

I cant speak of Nikon camera either as I have only ever used Canon, but certainly it is possible to view the brighter stars - even in my very light polluted garden, using the live view function. To get good goto I would use at least 4 alignment stars, maybe 5 and would perform the whole operation with the camera attached. I say this because the slightest knock or nudge from removing equipment in the focal train or accidentally kicking the mount will make all the effort you put in to making the goto accurate pretty pointless. Also it save you having to rebalance everything and again risk all the aforementioned issues, also you would be relying on your home position and return to target to be precise. You dont really want to be spending 20 mins looking again for something in the camera that you had already found.

Then try to stick to a sensible exposure limit say 20 or 30 seconds,play with the ISO settings ( I would go for quite high maybe 800-1600 whatever your camera is capable of)  take lots and lots of exposures and stack the best ones and you may surprised what can be achieved.

This is just how I would approach the method again if I were to go back to alt-azimuth imaging with your kit and from my own experiences, this is your party and you play it how you like as long as you have fun and enjoy your results thats the main thing.

Barry

Edited by Anweniel

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Thanks for a great reply Barry, I guess there is no harm in taking loads and loads of shot and just selecting the best.

When you refer to polar aligning, I cannot do this with an alt-az can I? I mean I could choose Polaris as one of my alignment stars but other than that there is no way to polar align that am I aware of? Also my mount will allow 2 star alignment at best, unless a firmware update changes that?

Sent from my HTC One S using Tapatalk

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Just to mention I have only actually ever aligned my scope once as I'm very new to all this but I have helped/watched a friend set up both an alt-az and an eq mount on several occasions, and have read a lot of articles and forum posts about both

Sent from my HTC One S using Tapatalk

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