Quick Question

[JohnSadlerAstro]

Hi,

I've been using a Canon DSLR for almost a year to take Deep-Sky photos, with a 200mm lens. I recently discovered that I can attach the cam to my telescope's eyepiece holder, and use the scope as a lens. The problem is as I'm still on an EQ2, my tracking isn't very good, so I have trouble getting a long enough exposure, even with loads of subs. Is there any trick that will allow me to get good photos until I can buy a better mount? ££££££££

John 

[Charic]

Hi there, have you heard of the 600 Rule? 

http://www.learnastronomyhq.com/articles/the-rule-of-600-in-astropho.html

or the 450 Rule! http://intothenightphoto.blogspot.co.uk/2013/05/my-450-rule-to-stop-star-trailing.html

......there are other numbers you can work with, google around, hopefully this may help your situation, until you better your tracking setup?

[swag72]

You can ensure that you have the best possible polar alignment and also I've read before of people either filling the tripod legs with sand or hanging something off the middle of the tripod to help with vibrations and overall stability

[JohnSadlerAstro]

Hi,

Is there any way of taking into account tracking in the 600 rule? I have been able to make around 10 sec on a still night without trailing.

John

[Charic]

.....I think the Rules are designed to allow you just to achieve a sharp image  from a stable platform, whereas with a properly setup and calibrated tracker/EQ, you could potentially leave the shutter open for  for as long as it takes, and still have pin sharp images.

[Charic]

38 minutes ago, JohnSadlerAstro said:

The problem is as I'm still on an EQ2, my tracking isn't very good, so I have trouble getting a long enough exposure.......

Are you just using the Slo-Mo controls to hold the target centre, or do you have a motor/clock drive?
If its Slo-Mo, then practice and practice some more, a driven unit would be more beneficial, once correctly polar aligned.

Another technique maybe, does your camera take movies, or do you have a web cam (often modified- filter removal and LED's removed?)  You can 'film'  the Moon for example, then stack the better  in-focus frames .

[JohnSadlerAstro]

Hi,

I do have an RA motor drive, which runs reasonably accurately, with new batteries.

John

[Charic]

..........you said your tracking isn't very good,  the motor runs reasonably accurate, and your having issues with long exposure?

If the system is critically aligned,  doubly checked, then the system should track effortlessly and maintain the target central to the sensor.
Long exposures themselves will be trial and error, until you find your base line. With your telescope, your using a fixed aperture and focal length, but with your other DSLR lenses, your exposure will be dictated by the lens in use, your ISO setting, aperture setting, and  the area of the sky your imaging. There are limits too that you may have already reached that are already beyond the cameras ability, or  even your own .
I've got a long-way to go yet before I go deep into Astrophotography, but at present my system is built around  a Nikon  5000 DSLR  not normally recommended here on the forums( not hust becauses its a 5000) but always seems to be a modified Cannon! as their sensors ( more so after modification) are better equipped for the task in hand.

Hopefully there will be  lots more feedback to better assist you with  your exposure issues. Who knows, maybe Santa! has a new EQ for you?

[wimvb]

If you can get good tracking at 10 secs, you should be able to image the brightest targets like the orion nebula (M42) and the pleiades (M45). Use high iso settings and take many subs (50+). Then take even more bias frames and also darks and flats. Carefull calibration and stacking will improve final results.

Use this to practice while you save for a better mount (maybe second hand).

Good luck.

[iapa]

21 hours ago, JohnSadlerAstro said:

Hi,

I do have an RA motor drive, which runs reasonably accurately, with new batteries.

John

Are you able to replace the batteries with a mains PSU? Then you will not suffer the same drop off in power to the motor. As per other suggestions, make sure your mount is level (I use a 3' long level, test the wee level itself is the same as a 6" long level, but it's heavier, and with the extended length the "balance" is better - my Sivel Injuneer Arkitetk daughter explained it to me once ), polar aligned and then loads and lots and lot and lots of lights, darks etc. as WIMVB said.

The rule of 600, the 400 rule etc. are sought guides as to when you can expect to see trailing on a static mount.

I'd setISO to max, take the 400 rule, that'd says 2 sec exposures, and try a few dozen lights, if they are good, try 2.5s, then 3s etc. When they trail, go to a lower exposure. Then drop from your max ISO, down a stop at a time until you get images you like. The the darks, flats etc.

There are some who suggest darks are not necessary when using a DSLR. I don't suppose it would hurt to take all your darks when its cloudy (why wast 'light' time), then you can try for yourself whether they actually make a difference or not.

Here enders the wisdom on the exspurt (ex - hasbeen, spurt - little drip; as defined un the Beano I think 50yrs ago.) who has yet to get anything decent in 3yrs trying this imaging lark.

 

[ollypenrice]

I'll go back to your original question,

I've been using a Canon DSLR for almost a year to take Deep-Sky photos, with a 200mm lens. I recently discovered that I can attach the cam to my telescope's eyepiece holder, and use the scope as a lens. The problem is as I'm still on an EQ2, my tracking isn't very good, so I have trouble getting a long enough exposure, even with loads of subs. Is there any trick that will allow me to get good photos until I can buy a better mount? ££££££££

...and reluctantly give you the unhelpful answer of no. Or at least, none that I know of. The reason is pretty simple. Your mount is limiting your exposures at your present resolution (= focal length with a given camera) to 'x' seconds. Beyond 'x' seconds you get elongation or trailing. If you increase your focal length then you will reduce 'x' seconds to less than 'x'.' Therefore in order to get an equivalent amount of light onto your pixels you will need a faster F ratio. But in reality your short FL lens is likely to have a faster F ratio than your telescope so your telescope is going to need better tracking (for its longer focal length) and  longer exposures (for its slower F ratio.) Double whammy.

If you are 'exposure time limited' by your mount the way to get more light in less time is through F ratio. You'd be better off looking for a faster F ratio than a longer focal length.  If there were a way to get around the need for a very accurate and very expensive mount for high resolution imaging you can be pretty sure we'd all be doing it... Imaging at F2 would be one way but super fast F ratios bring their own nightmares. 

So, sorry, I guess my own answer to your question is just, 'No.'

Olly

 

[RSM]

Hi, even with 10 second images you can still get a good result by taking lots and stacking them with darks, flats and bias. Doing that will also give you good practice for when you get a more stable mount.   The same techniques can be used on longer exposures for less bright targets.