Do I really need a guidescope? Would a CG3 suffice for some astrophotography?

[LaunchPhotog]

Hello

I am pretty new to astronomy, I have been doing visual observations for a while now, but I have been really becoming interested in shooting some long exposures of nebulae and galaxies, and some imagery of Earth orbiting satellites. I really don't want to spend that much at this point in my life, I am only 14 so going $1500 for Advanced VX with an auto guider unfortunately won't work out lol. I do have a DSLR and I do have a lot of experience with launch photography and DIY rigs, so I was wondering if I really needed an autoguider for maybe about 30 seconds or so on an exposure if I bump up the ISO to maybe 1600. And I know the CG3 is a really cheap mount, but if I was to buy one of the Astromaster telescopes and put a decent OTA on it, and I get the polar alignment perfect, is it doable? If I could modify the mount or motor drive itself that could also work, I have experience with Arduino systems. I really want to try to get a telescope soon because my family is going on a vacation to the Big Island of Hawaii for a week or so and the skies will be amazing, maybe even a few nights on Mauna Kea with no atmospheric distortion  . I just really would appreciate any input on using the CG3 mount with maybe slight modifications and a new OTA, and maybe how long I can expose the images without the stars trailing off. I do know that a DSLR's sensor is too large for Earth orbiting satellites, so I was thinking maybe completely tearing apart a USB webcam and modifying it to work with the OTA as well.

Thank you!

Alex Polimeni

www.alexpolimeniphotography.weebly.com

[kens]

If you get a good polar alignment that will reduce the declination drift. But you will still have periodic error in RA which puts a limit on your exposure time. That's where autoguiding comes in. How long an exposure you can get depends on the magnitude of the periodic error and your focal length. 30 seconds is not entirely out of the question but is at the upper end of the range at, say, 700mm FL. Leave your ISO at whatever value gives unity gain. Just take lots of subframes at whatever exposure you can get away with and stack them.And consider widefield photography with the camera on the EQ mount with a shorter focal length lens rather than through the OTA. If you've not one astrophotography before you'll probably get some usable shots that way. Otherwise you could spend all your time just working out what to do.

[Physopto]

It is not the DSLR sensor that is too large. Changing to smaller sensor will not magnify the image. You will just image a smaller portion of the light coming through your scope. Think of the light as a disc at the imaging point. If you reduce the size of the sensor on the disc the rest is wasted. To magnify the image you will need a bigger scope or a Barlow, or both. You need to match the scope image circle to the camera sensor.

Spend some time checking this out for yourself and please Do Not Rush. Many a mistake made in haste!

You may not have enough time for an informed choice before your holiday, but rushing into a purchase could be a complete disappointment for you, both from the monetary and astronomy aspects.

Derek

[hjw]

Hi Alex,

There are a number of factors which make a good mount like sturdiness and the quality of the drive train. I am afraid that the CG3 will not really qualify for any of these. Celestron sells a single axis motor for the mount, so with the motor attached and a good polar alignment it should be possible to take widefield images with the DSLR and a prime lens. Unfortunately, I have no experience with the quality of the motor and can not give you guidelines on how long you can push your exposures. But 30sec with a shortish tele lens should be possible. The longer the focal length, the shorter the possible exposure time. Take many shots and stack them with stacking software (Deep Sky Stacker is popular and free ).

By the way, there is a difference between tracking, where the mount follows the movement of the stars and guiding, where a secondary scope/camera sends signals to the mount to correct for deviations from the ideal tracking movement. You won't have to worry about guiding for a while.

And I do like your rocket pictures!

Good luck

HJ

[ronin]

You do not need a guide scope, however you will then need to do better polar alignment. You will likely then be limited to 60-120 second exposures - that makes me wonder if it is actually better to be a bit limited as a DSLR is not really suited to long exposures and the sensor gets warm/hot and then need to cool. The feature of NR on a DSLR will double the exposure time and so doubles the cool down between exposures.

As to the mount, it looks a bit lightweight, although I see the tripod in 2 forms and I suspect the tubular legs are better otherwise it seems to be an EQ3-2 match.

A lot will depend on the scope that you intend to put on, what often happens is that to see anything a person picks a visual scope and they are too big. The situation is along the lines that a 66mm ED refractor and DSLR may be lightweight enough for some imaging, but to see anything yourself you want something more like a 130P reflector. You cannot have both.

[RikM]

The CG3 is the equivalent of the skywatcher EQ2. This would be okay for DSLR + 50mm lens and exposures of 30sec.

The CG4 is the equivalent of the EQ3-2. That is a much more capable mount. I regularly take 3min exposures with a DSLR+50mm lens with an EQ3-2 (I have upgraded the legs to steel pipe like the CG4) I used to get 60-90sec subs with a 750mm FL Newtonian and a DSLR on this mount.

[theghettostylus]

I have the eq3-2 with skywatcher 150p and sand filled legs and all that jazz and can get around 6 min exposure at the moment, there is coma on the outside stars but the centre star is pretty much spot on, I tried DSLR with my old eq2 but it just wasn't sturdy enough even with the 130 scope on. I'm not a serious astro guy but the eq3-2 does do a good job. Its a good mount to get your feet wet.

[LaunchPhotog]

Thank you all for the responses! So from what I am seeing, it is not a good idea to get the Astromaster right now. But I do have the Canon DSLR with a 300mm lens, maybe I can just get a motor driven EQ mount and the lower focal length then some telescopes may allow longer exposures. The EQ3-2 seems pretty awesome, but with the motor drive it is quite a lot. This mount from Orion Telescopes is a bit cheaper and includes the motor drive, I just don't know how it compares to the EQ3-2. At 300mm, an exposure of 30 seconds to 1 minute would be nice, but I don't know if it is doable. And for satellite tracking, like the International Space Station, and even planetary imaging, would it be a good idea to modify a webcam for these or just use my DSLR? I have tried my DSLR with Jupiter and Barlows and it came out really small in the picture, but I don't know if I was doing something wrong. For satellite and planetary imaging I already have a reflector telescope on an Az-Alt mount so I think that may be better for those operations.

[Knight of Clear Skies]

The mount you've linked to doesn't have a polar scope I'm afraid, which would only make it suitable for driving a camera at very short focal lengths, maybe up to about 50mm.

Have you considered buying 2nd hand at all? I was able to pick up my Eq3-2 with RA motor for £120 + postage, then got a polar scope for another £20. I think the longest I've managed is about 75 seconds with a 200mm lens. It's not the best mount for imaging due to periodic error, I end up discarding a fair number of subs, but is pretty good for lens imaging. Here's one of my shots taken with an old 135mm lens:

And here's Orion at 50mm:

[theghettostylus]

If you go on AstroBoot.co.UK and click on specials they have the eq5 plus polar scope for £165 but they only have one, I paid almost that for my eq3-2 wish I had seen that first I would of had it. Go check it out.

[LaunchPhotog]

Wow, those are stunning photographs! I would love to produce images like that, I am considering the EQ5 and would be willing to buy a 2nd hand mount, but would I get improved accuracy with a motorized barn door tracker? I may be able to build something like that but I don't know if it is worth it.

[RikM]

Focal length is very important to consider. The longer your focal length, the more stable and precise your mount needs to be. A barn door tracker is perfectly okay for a DSLR with a 50mm lens. To get the big red nebulae, you would need to get the camera modified by replacing the IR filter with an astro-suitable one. This generally not that expensive, very much cheaper than buying a 60Da and you will get the exact same performance. It could well be easier to get a second hand pre-modified DSLR.

[Cornelius Varley]

If you go on AstroBoot.co.UK and click on specials they have the eq5 plus polar scope for £165 but they only have one, I paid almost that for my eq3-2 wish I had seen that first I would of had it. Go check it out.

Alex lives in the US and I don't think Astroboot post overseas.

[LaunchPhotog]

Yeah Peter, those links are to the UK for EQ3-2, I am worried they are going to cost a lot for shipping overseas, especially with the weight in the EQ mount.

[goose35]

Limited astrophotography isnt off limits. you will get more bad results than good to start but to start out its ok you will learn from mistakes better imo

i took these wide fields on a fixed tripod

http://stargazerslounge.com/topic/235923-my-first-go-at-astrohotography/

and these on my astromaster 130eq with cg-3 motor driven mount of M42

http://stargazerslounge.com/topic/22405-lets-see-your-1st-dsos/page-37  ( my posts on that page of M42)

I did modify the motor drive to use aa batteries rather than pp3 as they provide more amps for a longer period heres how i modded it

http://stargazerslounge.com/topic/235404-celestron-130-eq-md/

On a side note many prefer the SW130 over the astromaster 130 in hindsight they are probably right

[theghettostylus]

I think they would if you paid, I'm sure I read it in their t&c's even so I'm sure you can find a bargain where ever you live.

I noticed you lived in the US once I posted :0

[LaunchPhotog]

Ok, cool, I am seeing that I obviously need a strong mount to really do any meaningful astrophotography. I was talking to some people at my local astronomy club and I think I will be going with the Celestron Advanced VX 6 inch reflector, and going with a ZWO autoguider and Orion guidescope. Possibly also a polar finder, I don't know if that is necessary on the scope for an accurate polar alignment. I read somewhere that the telescope mount can help automate it so I don't know if it is needed.

THank you for all the help!

[Pompey Monkey]

Ok, cool, I am seeing that I obviously need a strong mount to really do any meaningful astrophotography. I was talking to some people at my local astronomy club and I think I will be going with the Celestron Advanced VX 6 inch reflector, and going with a ZWO autoguider and Orion guidescope. Possibly also a polar finder, I don't know if that is necessary on the scope for an accurate polar alignment. I read somewhere that the telescope mount can help automate it so I don't know if it is needed.

THank you for all the help!

Be aware that the Celestron Advanced VX 6 newtonian reflector apparently does not have enough back focus for a dslr. I've only done a very quick search as I have to go to work, but I think you need to check this!

[RikM]

Looking at the reviews on B&H photo, one reviews says DSLR back focus is fine and the very next claims it is not so I think it will depend on the DSLR backfocus distance. The drawtube appears to have a t-thread on it to attach a DSLR directly vis a t-ring, so no adaptor to worry about. My guess is that with a Canon at least it will be fine, but as above, it makes sense to check this with someone who actually uses one before purchase. Ask which camera model they use and how they connect it.

http://www.bhphotovideo.com/c/product/917580-REG/celestron_32054_advancd_vx_6_newtonian.html

[LaunchPhotog]

I appreciate it, I will contact them. There is always the possibly of buying an extender to the scope.