What am I doing wrong?

[pberrett]

Hi everyone

I recently bought myself a telescope and mount and have been trying to take images in a light polluted area.

First here's my setup

- Skywatcher 130P/900 telescope
- Synscan Alt/Az mount
- Electronic eyepiece SvBony Sv-205 8Mp (on 1280 x 720 setting)
- cheap light pollution filter

I have looked at the moon and a number of planets but now I wanted to try and image stars. I pointed my telescope towards Acheron and took 200 x 100ms exposures as an avi file and then later 200 x 200ms exposures as an avi file. I stacked both using registax but the best I could do was the following.

What am I doing wrong? Admittedly my area is fairly light polluted but I was using a light pollution filter with fairly long exposures.

Thanks Peter

[blink138]

200ms are very short exposures mate
stars 100's of times fainter than the moon
try a few second exposure perhaps?
pat

[Imme]

Extend your exposures and up the iso would be my advice

[pberrett]

Thanks for the replies.

It looks clear tonight so I will have a chance to try out your recommendations. Also as far as I know there is no ISO setting on a electronic eyepiece. I am using a Svbony sv-205 with AstroDMx software.

Can you suggest an exposure time to try? How long can I go before my stars become elongated or blur?

Thanks Peter

[xelasnave]

500 rule

https://petapixel.com/2015/01/06/avoid-star-trails-following-500-rule/

Alex

[pberrett]

Thanks

My telescope has an aperture of 130mm and focal length of 900mm so I presume the calculation is 500/900 = 0.55 seconds. Have I calculated this correctly?

Thanks Peter

[astro744]

This is the maximum exposure length before trailing is noticeable when tracking is not used. Note the 500 rule is only an approximation. Use the NPF rule (search NPF rule) for better accuracy. Note the trailing is less as the target is nearer the poles.

Which constellation is Acheron in? I have never heard of it being a star. Did you mean Achernar?

[Imme]

Sorry, thought it was a dslr.

As Alex states....500 rule is what you’re after.

Or,

Start with half a second, then 1 second......and keep going until you don’t like what you see.

[xelasnave]

I don't know I never use it..I just keep pushing the time until the stars are too eggy to tolerate.
But I think you are correct.
Good luck..let us know how it goes.
Alex

[pberrett]

My bad. Yes I meant Achernar. Its very high in the sky.

One complication in all this is that i am using a simle tracking mount (Skyscan) so that will probably mean I can have longer exposures.

Short answer to this is that its almost dark. Soon I will go outside, pick a star to focus on and then try a series of different exposures and see what difference they make.

At the end of the day I want to see how much fine detail and faint stars I can see in my images.

Once I have the optimum exposure time I will take sequences of images 12 minutes apart and see if I can find any new comets for asteroids. A bit ambitious for a light polluted area but no harm in trying!

Of course some will say that one needs a much bigger telescope to find asteroids and comets but there is some new software called Tycho which may make it possible to find asteroids using a smaller telescope. It stacks images in all different directions to identify faint asteroids.

cheers Peter

[xelasnave]

Try to the East of M74...although probably too much Moon..that's why I am not imaging it tonight..however there is/ was something there that was moving very slowly and left worm trails about a half centimeter long on screen after two different stacks of about 2 hours each...whatever it was it means I have to probably throw all that data out..or colour it in in the final process.
Good luck
Alex

[astro744]

The camera you have has a 4.5mm x 3.4mm sensor. (5.7mm across the diagonal. With your 900mm focal length telescope at prime focus you will get about 0.36 deg. field of view across the diagonal of the chip. This is very narrow for asteroid hunting.

Field of view (deg) = diameter or width of chip (mm) x 57.3 /focal length of telescope or lens (mm).

I believe the SV-205 has 3264 x 2448 pixels each 1.4microns across which equates to 4.5mm x 3.4mm (approx). or 5.7mm across the diagonal of the chip. A 90mm camera lens for example will give you 10x the field at 3.6 deg. (Or a sensor 10x the size such as a full frame DSLR or bigger. - DSLR not quite 57mm across the diagonal, only 43mm but you get the idea).

[pberrett]

Thanks

With cost considerations everything is a bit of a compromise. I am happy to accept a smaller field of view because I was able to purchase an as new skyscan mount + 130P/900 newtonian for just $430 total which I think was a good deal for a beginner starting out.

Down the track I am considering purchasing a second hand full frame dslr which would improve things a bit. But first I need to get my hands dirty to see what kind of performance I can get out of my telescope.

At some point over summer I will take my gear out to Warburton where it is much darker and do some astrophotography there. Its light profile is similar to Lancefield where I grew up and I have vivid recollections of how amazing the night sky looked out there.

cheers Peter

[pberrett]

Well... and now for the results or rather no results.

Pretty good nice for some astro but when I tried to set my svbony sv-205 to take an exposure longer than 1000ms I got a message from AstroDMx saying that the camera is only capable of doing 5-1000ms!

I guess this means that the camera is only good for planetary exposures which is both a surprise and a shame. I shall look around on the Internet and see if there is any information about this but failing that my next step is a second hand DSLR.

cheers Peter

[Pepper]

Chunkywheeler has a very cheap canon 450d for sale in classifieds at the moment. Be a good beginner dslr.

[xelasnave]

Grab the 450d
Alex

[raymo]

I suggest that you find a 550D or 600D with the articulated screen, not much
difference in price, but makes life soooo much easier; no more cricked necks.
raymo

[pberrett]

Hi

Actually its a 400d but that will be adequate to get me started, I note also that there is a firmware upgrade available that will allow the use of an intervalometer.

I have PM'd Chris

Thanks Peter

[xa-coupe]

I have an SVBony 205 .. it has the sensitivity of a house brick. It's okay for looking at the moon but I'd chalk it up to experience and go and get something else such as a DSLR. You can return to the 205 when you've a handle on it all and decide to get something else anyway !!

[Sunfish]

Second the articulated screen!

[Outcast]

I agree, articulated screen is a must unless you like bending your body into bizarre positions, particularly if you eventually upgrade to an EQ mount.

Whilst not quite as cheap as the 400d on offer in the classifieds, a quick perusal of Gumtree & Ebay indicates a 550d can be had for $250 to $300 depending upon accessories included...

Cheers

[pberrett]

Thanks

I have already emailed and said I'll buy the 400d if available but I will note the advice. I also have just ordered a Raspberry Pi High Quality camera so I expect I will be able to shoot images with that as an alternative. I can adjust that setup how I like.

cheers Peter