Can't reach focus with explorer 200 PDS and canon 550d

[Jannis]

Hi.

I just got this telescope on a HEQ5 pro mount, as an upgrade from my skywatcher capricorn 70mm, and what a difference...

But, i have a problem, i can't reach focus when i connect the camera directly to the 2" adapter with the T ring. no matter how far in or out i moove teh focuser, all i can see in teh camera display, is the 2. mirror and the 4 mirror supports.

I thought the 200 PDS was made to be easier to reach focus, as i know it was a problem on the 200P, but i still don't get anywhere.

Any ideas on what i should do?

Anyone have a pic of how the whole thing Should look on this telescope with an slr attached to reach focus?

I've attached pics of how it looks with the camera attached and the focuser all the way in and out. as you can see, focuse isn't exactly on the stars...

Thanks.

[Jannis]

Forgot to mention, Jupiter was right in the center there.

BUT! Now, this is embarrasing, but it seems i kind of forgot to take away the 2" extention tube on the focuser. I guess working outside in -19c slows your brain down a bit, hehe.

So it might be just that. However, i just tried it indoor, towards the house accross the street (roughly 35 meters), and it Barly didn't focuse all the way out without the extention tube. so i put it in, and it did indeed focuse.

But, i never got to replicate the first pic i got outdoors, with focus on the 2nd mirror. weird? o.o

[sixela]

It's all normal. Close objects focus with the focuser racked out a lot more, and 35m is a lot closer than Jupiter .

If you're interested:

1/(focal_length_telescope)=1/(object_distance)+1/(image_distance).

So, as you can see, objects at infinity focus on the focal length, objects at twice the focal lenght focus at their own distance, and everything in between,...

[Black Knight]

Aha! This is a common problem that I originally suffered from with a couple easy solutions, and a couple of harder solutions

1. Easy: Use a barlow lens. This will work although reduce the amount of light reaching the cameras sensor.

2. Easiest solution: Use the direct camera connection. I didn't even know this existed until someone on SGL pointed me in the right direction. I'm not sure if your focuser has this. My focuser is the standard Crayford with the 1.25" adapter. On my focuser, unscrew the barrel of the 1.25" adapter from the focuser to reveal the direct camera connection, and attach your cameras T-ring directly to it.

3. Use a SkyWatcher Coma Corrector and adapter to attach the camera.

The more difficult solution is to move the mirror further up the tube, towards the secondary.

I went for the easier solutions

[Black Knight]

Ahh.... just read your second post .... you have it sorted now?

[Jannis]

Thanks.

I know it's a bit different distance, hehe. But i still do not get why i got a clear picture now without the 2nd mirror in the way, wich i did outside with the focuser at the same position? I mean, at worst i should have gotten a black picture as the stars didn't focuse, not a picture of the 2nd mirror and the inside of the tube?

But i'll try some more as soon as the clouds go away (in a few days they say, doh). Probably something very basic and stupid i'm overlooking, as it worked indoors now..

[Jannis]

Ahh.... just read your second post .... you have it sorted now?

I'm not sure, but i think so. I must have done something very wrong out in the cold Still a bit confused about how i managed to get focuse Inside of the tube like on the first pictures, when it worked perfectly when i tried it how. Have yet to try it at the sky though. maybe if the clouds go away enough so i can try at the moon i will give it a try and see what happends.

But, about what you said, on teh 200 PDS the mirrors are supposed to be a bit closer to each others to avoid exactly that problem, so i can't see why it would be needed to moove the morrors even closer. But, i'll see what happends. I'll give it another try as soon as it's clear sky.

Thanks for the advises guys!

[Black Knight]

But, about what you said, on teh 200 PDS the mirrors are supposed to be a bit closer to each others to avoid exactly that problem, so i can't see why it would be needed to moove the morrors even closer. But, i'll see what happends. I'll give it another try as soon as it's clear sky.

Yeah, sorry, I forgot that on the PDS the secondary is already positioned closer to the primary!

[Jannis]

well, the moon is now up, but so are the clouds still. and here in norway it's already midnight now, so have to give it a try some other day. next evening with clear sky is tuesday, and temperature down to -22c. Not looking forward to it with those temps, but hopefully it might be worth it.

[Jannis]

Ok now, finally clear sky, sort of. almost storm in the wind though, but didn't stop me from trying. focus is working correctly, and here's my first galaxy pic, after a quick run through dss.

so, concider this case solved.

[brantuk]

Great result Jannis

[Neo_uk]

nice first attempt jannis.

you might want to throw the original data in to photoshop and process the image a bit more im sure theres a lot more detail to be had from from it.

i had a very quick play with the jpeg of andromeda you posted in this thread (i hope you dont mind) but there is only so much you can do with a jpeg (always shoot in raw and process in raw).

chris.

[Jannis]

Thanks. Looks quite a bit better.

this is a bit off topic i guess, but.

I have to admit, i'm unfortunally a complete newb when it comes to PS. i have it, but barly knows the very basic stuff.

i guess the ~100MB 16 bit TIF file will do, right? or did you mean to work on each raw files in PS first before stacking them?

[Neo_uk]

Hi Jannis,

Stack all your raw files with dss and then save file as tiff and then open the tiff in photoshop and work on it there.

The main things to play with are the curves and levels.

Curves will lighten the image extract the details but will also heighten other things then you reduce these with the levels adjusting each channel rgb be careful not to clip into the info though.

you will see as you play around but if in doubt there are some very good tutorial videos on youtube.

hope this helps.

regards chris.