Why cant I get my camera into focus anymore

[Mistasparkaru]

Well thats another night wasted, faffing about in the cold

I just cant seem to focus my canon eos 450d connected to my meade lx200 12" classic.

Im trying to use apt to help, i used to get below 2 on the fwhd without even trying but now it fluctuates all over from a blobby 4 to 6 and up.

I just bought a bahtinov mask to try to help but its so bad i cant even see the spikes and apt just fluctuates from close to far and all over.

I have tried with and without my focal reducer but its still the same

I can focus using a 90 and 30mm ep and the view is great so i dont think theres anything wrong with the telescope

I can also use the collimation cicles in apt and once i have de focused the "donut" fits perfectly so i dont think im out of collimation

I had started to get some nice pictures but this has really stuffed things up as i dont know whats gone wrong.

I have bought a dew heater as the weather does seem wetter but i havnt had chance to use it yet

[jambouk]

You say you have managed to achieve focus with this scope and this DSLR previously, so you have proven that combination works.

The scope sounds ok as you've checked collimation and can achieve focus with an eye piece.

Is the camera ok? Have you out a camera lens on it and checked that side of things? Will it allow you to achieve focus looking just through the camera and a camera lens at something 10 feet aeay?

Can you see a pin point of light on the canera when connected to the scope? Or does it not even get that well focused? Does it look roughly focused to you but the number is just not as tight as before? If so, has the scope had chnace to full cool down (2 bours i suspect with that beast if it's been stored anywhere remotely warm); is there any dew anywhere between the star and the cameras sensor; what is the seeing like???

I suspect the issue is a seeing / cool down one, but you need to exclude the other aspects too.

James

[Guest]

Good morning from Vienna,

I also have a Canon.. and something I did learn.. the BACK-FOCUS is the main and most important matter.. Did you also calculate the BACK-FOCUS Distance "The distance between the back of a lens and the image of an object at infinity."  and consider also the Back Focus of your  Reducer + Canon? so you reach the perfect FOCUS ?? and get ROUND STARS ?

Just a hint !! I also have had same problems, and the reason was, 10mm adapter was missing in my calculation !

Regards and good luck

Martin

[Mistasparkaru]

Hello james, its james here too

Would it really take 2 hours to cool down? I keep my setup in an astrono-shed the only part i keep in the house is the camera.

I can almost focus using the cameras focuser but the stars go from unfocussed-blobby circle-unfocused

Im starting to suspect due as well, as it was dry last time i got good focus, i thought the setup was seeled and the only part that due could collect wouldbe on the collector.

I will try out the camera today

[Mistasparkaru]

Ah yes i did think about back focus last week as i have not been able to get decent focus for a few weeks now.

From my googling i think my f6.3 meade 4000 focal reducer needs 105mm to be in focus this seems about right after eyeing up with a ruler... Ive tried without the reducer as well and its still the same

[jambouk]

Have you ever achieved sharp focus?

James

[Mistasparkaru]

Not what id call pin point sharp i have achived 1.6 fwhm and the stars were reasonably small discs. It was good enough that i was happy with the pictures but had do do cropping to get rid of the worst but had put the worst ones down to vignetting

[jambouk]

What I am trying to establish is whether your system will allow precise focus, but recently something has gone wrong, or is there a problem with your system and without some adjustments / extra kit, you'll not be able to achieve focus.

Have you ever been able to take a star which is out of focus, tthrough where it looks to be in focus, and back out the other side of focus again? If so, your sustem will allow focus to be achieved - and if your scope is an SCT, i'f have thought this is the case.

Assuming you should be able to achieve focus, then the issues are as per my original reply.

- cool down; if the scope is kept cool anyway, then it is unlikely to need 2 hours to cool down, but if it is warm (central heating, hot shed) then it may well take 2 hours to get to ambient temperature.

- seeing; i'm not sure where you live, but if the jet stream is iver head, the seeing will be poor and stars will be very twinkly, and precise docus difficult to achieve. What time frame is your fwhm number being generated over? If very short then the number will be jumping up and down.

If you've never had precise focus, or can't travel in and out of best focus by turning the focus know one way, then there is a problem.

James

[jambouk]

I still suspect a hot scope and poor seeing.

James

[Mistasparkaru]

I can go right through focus i.e if i turn the focuser all the way left and slowly turn it right i will go through unfocused-donuts-round stars-small round stars-round stars-donuts-unfocused

So the scope can reach the focal distance its jjust i can no longer get it into sharp focus

The seeing is great, last night i could see andromeda by eye

[Scooot]

is your focusser slipping. Or maybe dew or condensation?

[Mistasparkaru]

Ok ill admit when iv been a pilok.... The camera was set to 30sec +iso 1600 i didnt realise that apt tried to stack liveview to make it look like a 30 sec exposure

I was trying to focus an over exposed blob

[jambouk]

Glad it's sorted.

James