75-300mm focus problem

[Atreta]

hi,

i just got a brand new canon 75-300mm lens and i can`t seem to get it to focus properly to infinity at 300mm fl. i tried with a distant illuminated statue in a mountain peek over here, the statue gets focused, i then pointed to the moon, autofocus confirmation was beeping to confirm it is in focus, but the picture doesn`t look sharp to me. first i thought it could be motion blur, so i tried to use a faster shutter speed to avoid it.

this is one of the pictures i tried to take, is it ok?

thanks in advance.

[RT65CB-SWL]

This may appear stupid, but have you tried manual focus?

[Atreta]

Thanks for the reply, yes i did try and it stays the same. I also tried yesterday with jupiter and couldn't focus it at all using apt in live view. 

[Buzzard75]

I use manual focus with mine. Auto is pretty much useless at night. Use manual and in live view increase the zoom on the screen by 10x. Go into live view and then in the upper right hand corner on the back of the camera, there should be two buttons with blue magnifying glasses below them. One has a + and the other has a - in the magnifying glass. Press the one that has a + twice and it will go to 5x and then to 10x. Press it once more and the live view will return to 1x. When in 10x, focus until the star is as small as possible or you get sharp focus on the moon. It's really the best way to try and get focus on the moon or stars. If you're willing to spend some time/money, you can make/buy a Bahtinov mask or a Y mask for your lens. You can also purchase some software like BackyardEOS that has a FWHM mode that will help you achieve focus.

[PeterCPC]

....or use a Bahtinov mask.

Peter

[SteveNickolls]

19 hours ago, Atreta said:

i just got a brand new canon 75-300mm lens and i can`t seem to get it to focus properly

Hi Atreta, thanks for your post. Not sure which Canon lens you are using, I have the basic Canon EF 75-300mm f/4.5-5.6 III USM and at 300mm I find I have to stop it down to prevent odd star shapes occurring. I have not noticed any slippage of the lens during a session. At 300mm you should be able to manually focus very well using a bright star or far away street light. Take your time going into and out of focus until you are certain you have the best focus. Don't rush this step. As Buzzard75 notes you should employ the magnify function on the camera (once you have the star in the centre of the 'Live View' screen) to best judge focus.

Good luck with your future imaging.

Best regards,
Steve

[Atreta]

17 hours ago, Buzzard75 said:

I use manual focus with mine. Auto is pretty much useless at night. Use manual and in live view increase the zoom on the screen by 10x. Go into live view and then in the upper right hand corner on the back of the camera, there should be two buttons with blue magnifying glasses below them. One has a + and the other has a - in the magnifying glass. Press the one that has a + twice and it will go to 5x and then to 10x. Press it once more and the live view will return to 1x. When in 10x, focus until the star is as small as possible or you get sharp focus on the moon. It's really the best way to try and get focus on the moon or stars. If you're willing to spend some time/money, you can make/buy a Bahtinov mask or a Y mask for your lens. You can also purchase some software like BackyardEOS that has a FWHM mode that will help you achieve focus.

Thanks, buzzard75, I did try jupiter with APT, but i was looking quute odd. I'll wait for the full moon to give it a try again. The Y mask is a nice suggestion. 

13 hours ago, PeterCPC said:

....or use a Bahtinov mask.

Peter

Thanks, Peter, yes a bahtinov mask would make things easier, or a  Y mask as buzzard75 suggested too. 

[Atreta]

1 hour ago, SteveNickolls said:

Hi Atreta, thanks for your post. Not sure which Canon lens you are using, I have the basic Canon EF 75-300mm f/4.5-5.6 III USM and at 300mm I find I have to stop it down to prevent odd star shapes occurring. I have not noticed any slippage of the lens during a session. At 300mm you should be able to manually focus very well using a bright star or far away street light. Take your time going into and out of focus until you are certain you have the best focus. Don't rush this step. As Buzzard75 notes you should employ the magnify function on the camera (once you have the star in the centre of the 'Live View' screen) to best judge focus.

Good luck with your future imaging.

Best regards,
Steve

Thanks, Steve,  it is the same lens as yours. I'll try to stop it down next time.

Btw, do you guys happen to have any pictures of the moon taken with it?  

[Buzzard75]

Did this one a few weeks ago during the blue moon in March.

[Atreta]

Thank you again,  nice moon picture. 

When I get to test the lens again I'll post here the results. 

[Thalestris24]

Hi

Are you making use of the APT focus tool with the camera, and lens set to manual? It's probably the best way to get focus. Also, the Moon isn't easy to focus on so focus on stars then slew to the Moon. Also a TeleFocus75 is quite useful but not sure about availability in Brazil (and they're expensive for what they are).

Louise

[Atreta]

Hi Louise,

when i tried to focus on jupiter i used apt in manual mode and zoomed in all the way, but didn't use the focus tool. I tried to take some test pictures of stars too with apt, it looked nice, but i deleted it all. When the weather clears i'll try to focus on Gacrux companion star as it is much fainter and a good focus reference, or maybe Jupiter's  moons too.

That focuser is interesting but yes, very expensive and having to import it is a no go because of the exchange rate  and import fees.

thanks a lot,  i'll post soon the next results ( hopefully good ones)

[SteveNickolls]

10 hours ago, Atreta said:

Btw, do you guys happen to have any pictures of the moon taken with it?

Hi Atreta, no moon photos I'm afraid as I image DSO's :-(

I do have an image taken with my Canon 600D and the lens at 300mm (see below) and the entry for my astronomy log for that night  is relevant to your focus issue-"This evening the sky was clear so I again set up the same equipment and tonight took images of the Perseus Double Cluster and Stock 2 open cluster. In total I captured 20 light frames of 180 seconds duration plus 10 dark frames. Imaging was done using the Canon 600D DSLR and 75-300mm lens at the 300mm FL setting, ISO 400 and f/6.3. I had initial focus issues which I was able to resolve by reducing the lens from f/5 to f/6.3. The focus was giving strange shapes to the stars. After the first 10 light frames the mount hardly showed any movement even between 5 successive exposures. Imaging concluded at 11.43 PM."

Image composed from 20 x 180 second light frames at ISO 400, f/6.3 and x10 dark frames plus x50 flat and bias frames. Stacked in Deep sky Stacker and processed in StarTools. The mount was my Star Adventurer.

Hope you have lot of opportunities on the coming evenings to experiment under with your camera.

Best Regards,
Steve

[John78]

On 4/21/2018 at 23:18, Atreta said:

hi,

i just got a brand new canon 75-300mm lens and i can`t seem to get it to focus properly to infinity at 300mm fl. i tried with a distant illuminated statue in a mountain peek over here, the statue gets focused, i then pointed to the moon, autofocus confirmation was beeping to confirm it is in focus, but the picture doesn`t look sharp to me. first i thought it could be motion blur, so i tried to use a faster shutter speed to avoid it.

this is one of the pictures i tried to take, is it ok?

thanks in advance.

That looks in focus to me, what you're used to seeing on here is stacks of lunar images not just single frames which are then sharpened, I suspect that's why your frames seems soft.

Your technique for focusing should work OK, using manual focus will also work - but I think if you took 200+ of those lunar images and processed them using registax or autostakkert you would get the result you expect.

[Buzzard75]

59 minutes ago, John78 said:

That looks in focus to me, what you're used to seeing on here is stacks of lunar images not just single frames which are then sharpened, I suspect that's why your frames seems soft.

Your technique for focusing should work OK, using manual focus will also work - but I think if you took 200+ of those lunar images and processed them using registax or autostakkert you would get the result you expect.

Actually, my moon image I posted in this thread was a single exposure. I don't recall off the top of my head, but it was something like 1/200s and ISO100 stopped down to f/8 using my Skyguider Pro for tracking.

[John78]

Your single frame is in focus (see below).... So next time you go out take several hundred frames and stack them - it will fix the noise and also seeing issues so you will get a much much better picture.

 

If its possible with your DSLR you want to lock the mirror up and take the frames so the shutter actuation doesn't keep shaking setup.

 

[Atreta]

6 hours ago, SteveNickolls said:

Hi Atreta, no moon photos I'm afraid as I image DSO's :-(

I do have an image taken with my Canon 600D and the lens at 300mm (see below) and the entry for my astronomy log for that night  is relevant to your focus issue-"This evening the sky was clear so I again set up the same equipment and tonight took images of the Perseus Double Cluster and Stock 2 open cluster. In total I captured 20 light frames of 180 seconds duration plus 10 dark frames. Imaging was done using the Canon 600D DSLR and 75-300mm lens at the 300mm FL setting, ISO 400 and f/6.3. I had initial focus issues which I was able to resolve by reducing the lens from f/5 to f/6.3. The focus was giving strange shapes to the stars. After the first 10 light frames the mount hardly showed any movement even between 5 successive exposures. Imaging concluded at 11.43 PM."

Image composed from 20 x 180 second light frames at ISO 400, f/6.3 and x10 dark frames plus x50 flat and bias frames. Stacked in Deep sky Stacker and processed in StarTools. The mount was my Star Adventurer.

Hope you have lot of opportunities on the coming evenings to experiment under with your camera.

Best Regards,
Steve

Thanks a lot,  i forgot to try to stop down the lens. With my vintage 135mm f.2.8 lens i have to stop it down to f5. 6 to avoid chromatic aberration. Nice log. I should start making sims kind of notes too.  Weather this year is not giving much opportunities. 

[Atreta]

2 hours ago, John78 said:

Your single frame is in focus (see below).... So next time you go out take several hundred frames and stack them - it will fix the noise and also seeing issues so you will get a much much better picture.

 

If its possible with your DSLR you want to lock the mirror up and take the frames so the shutter actuation doesn't keep shaking setup.

 

Thanks, John. I was in doubt if it was in focus because the bottom looks soft compared to the upper part. The shot was handheld, it was just some test pictures. Next time I'll use it on the heq5 and record a video to stack later. I have some moon pictures i took with the telescope, but didn't find it to compare the sharpness with that one. 

[John78]

4 minutes ago, Atreta said:

Thanks, John. I was in doubt if it was in focus because the bottom looks soft compared to the upper part. The shot was handheld, it was just some test pictures. Next time I'll use it on the heq5 and record a video to stack later. I have some moon pictures i took with the telescope, but didn't find it to compare the sharpness with that one. 

I think its OK - you'll get much better images using a HEQ5, but depending on how long you have in your imaging session shooting many images would yield better results than shooting in video mode.

[alacant]

Hi. My method. As my 700d will autofocus on the moon 

• set to Av f8 
• Set Auto on the lens
• Partially press the shutter
• Tape the focus
• Tape the zoom
• Set Manual on the lens
• Set to M on camera

 That's it. HTH.

[Buzzard75]

Here's another one I took just last night.

 

[Atreta]

8 hours ago, alacant said:

Hi. My method. As my 700d will autofocus on the moon 

• set to Av f8 
• Set Auto on the lens
• Partially press the shutter
• Tape the focus
• Tape the zoom
• Set Manual on the lens
• Set to M on camera

 That's it. HTH.

Thanks, Alacant. As soon as weather breaks I'll try it. 

[Atreta]

4 hours ago, Buzzard75 said:

Here's another one I took just last night.

 

Nice picture, weather is kinda bad these days in here, so i wasn't able to try again. 

[Buzzard75]

Thanks. My one complaint about this lens is probably the finicky focus. It's difficult to rotate the focus ring and make small adjustments. Not sure how they would go about implementing it, but a fine and coarse focus ring similar to a two speed Crayford would be amazing on camera lenses. Especially when a hair one way or the other can throw things off horribly. Stick with it though. Hopefully you'll get some clear skies soon to try again.

[Thalestris24]

2 minutes ago, Buzzard75 said:

Thanks. My one complaint about this lens is probably the finicky focus. It's difficult to rotate the focus ring and make small adjustments. Not sure how they would go about implementing it, but a fine and coarse focus ring similar to a two speed Crayford would be amazing on camera lenses. Especially when a hair one way or the other can throw things off horribly. Stick with it though. Hopefully you'll get some clear skies soon to try again.

Hi As mentioned above these are available though a diy hack might be possible and would certainly cheaper!

Louise