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Can’t focus with DSLR


CraigB86
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Hi all.

I recently invested in a star adventurer and finally had clear skies tonight to try and get some imaging done. Or at least that was the plan! I couldn’t gain focus at all. I tried everything (I think). Used live view, manual focus. I tried using two different lenses - the stock 18-55 lens and 75-300 lens. It almost seemed as if when I was trying to zoom out to gain focus the lenses reached their limit before focus could be attained. 
 

im using a canon eos4000d with stock lenses. I’ve attached images of what the live view was showing when trying to focus on Vega and my results when shooting.
 

many thanks!

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88A72439-78D2-404C-A9DE-F6D0CC691553.jpeg

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I always found trying to focus with a DSLR/lens very finnicky. I also found that setting the lens to 'infinity' very often was not 100% accurate.  Best advice I can suggest is turn AF off and just use manual focus, set to infinity and be prepared to adjust the focus ring a tiny amount each time. I once used a 70-300 on a Pentax DSLR and ended up making my own Bahtinov mask to achieve focus but even then it was a faff.  You might struggle with an 18-55 unless you can zoom right in on live view?

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I agree.  Use manual focus and a Bahtinov mask if you can, though I also found it was quite awkward getting focus unless I connected the camera to a PC and controlled it using APT or something similar.

James

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Thanks both. I’ve not got an infinity setting on either of my lenses. I’ll have a look at a Bahtinov mask and I think I’ll also try autofocusing on something far away to get focus then switching back to manual before I shoot. 
 

fingers crossed!

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You have to use manual focus in live view.  Turn  OFF image stabilisation. Turn up the ISO as high as it will go and focus on a star or stars using live view 5x. Leave the focus setting there or better still, tape the lens focus ring so it can't move.  Go back to the ISO setting of choice for your capture.

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I’m an idiot. I was trying to gain focus by turning only the base of the lens & didn’t realise the end could be turned for more precise focus! 🤪

just need to wait for another cloud free night so I can try again!

thanks to everyone for your advice!

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58 minutes ago, CraigB86 said:

I’m an idiot. I was trying to gain focus by turning only the base of the lens & didn’t realise the end could be turned for more precise focus! 🤪

just need to wait for another cloud free night so I can try again!

thanks to everyone for your advice!

Happens to us all :) I have forgot to focus at all before now. I have been very impressed with my framing. Carried out all the subs and darks then realised I never checked the focus!  My usual one now to forget is checking the histogram. The amount of times I have focused, done my test shots then totally forgot about checking the histogram before then taking all the subs.

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You have a nice bright image of Vega even if it's very out of focus. You should have no trouble finding decent focus if that's what you are starting with. With my Nikon D3200 I need to be pretty close to focus before I see anything on the live view.

I definitely recommend sticking down the focus ring with tape - it's the one thing that has wasted more time for me than anything else when imaging using the DSLR with kit lens. Focus on bright star, slew to the target, take a test shot only to discover it's out of focus. Trying to focus on a nebula or galaxy with a 55mm lens is almost impossible - far too dim. If only my focus ring had a locking screw like my telescope does :(

Of course, that's not to mention the dreaded D word ... dew!

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