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Tips For Dslr Focussing


Dazzyt66
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Hi,

I'm trying out my first steps into AP using an ST80 and an unmodded Canon 1100d. I had some good experimental shots so far with M45 and the moon and am starting to get the hang of DSS for the star based shots (I've got some Orion nebular shots from the other night that look promising.

One thing I a struggling with is focus. The screen on the camera seems ok for bright objects but pretty useless for stars which leaves me with the viewfinder which seems a bit hit and miss to achieve that perfect focus.

I haven't tried controlling the camera through the laptop yet (although I do know how to do it) so is that the answer? I wanted to try and keep as portable as possible because when I say AP, at the moment (

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During your focusing routine, ensure the ISO setting is at its highest. For example on my 60d I set it at 6400. Then find a reasonably bright star and focus on that using live view and the 10 X zoom setting. For the icing on the cake buy a Bahtinov mask to ensure crisp focusing. Once you have done that lock your scope focuser if it has that function and return the ISO setting of your camera to your choice for the shots. Another tip is to place the star about 1/3 distance from the centre of the screen when focusing.

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The best thing I have found is using my 7 inch android tablet running dslr controller connected direct to the 1100d using and otg cable into the canon USB cable into the camera. Can control the camera totally and focus easy as what camera sees is shown on the tablet and can zoom in on a point x5 and x10.

Imagine the image with a line a third in from each edge. Where the lines intersect on a corner is a good place to find a star to focus on.

Edited by happy-kat
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Hi

You probably won't be able to achieve perfect focus with the ST80 simply because it's a fast achromat which also suffers from a lot of field curvature. I found that attaching a SW autofocuser was a great help. Also, although I've never tried it, the Startools 'Lens' function can compensate the distortions caused by field curvature.

Louise

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During your focusing routine, ensure the ISO setting is at its highest. For example on my 60d I set it at 6400. Then find a reasonably bright star and focus on that using live view and the 10 X zoom setting. For the icing on the cake buy a Bahtinov mask to ensure crisp focusing. Once you have done that lock your scope focuser if it has that function and return the ISO setting of your camera to your choice for the shots. Another tip is to place the star about 1/3 distance from the centre of the screen when focusing.

+1 for the Bahtinov mask.

Peter

The best thing I have found is using my 7 inch android tablet running dslr controller connected direct to the 1100d using and otg cable into the canon USB cable into the camera. Can control the camera totally and focus easy as what camera sees is shown on the tablet and can zoom in on a point x5 and x10.

Imagine the image with a line a third in from each edge. Where the lines intersect on a corner is a good place to find a star to focus on.

Hi

You probably won't be able to achieve perfect focus with the ST80 simply because it's a fast achromat which also suffers from a lot of field curvature. I found that attaching a SW autofocuser was a great help. Also, although I've never tried it, the Startools 'Lens' function can compensate the distortions caused by field curvature.

Louise

Thanks guys for the tips. Defo gonna get a bahtinov mask as that seems the easy fix.

Happy-Kat - I don't have android but I can use the live view software from canon on the laptop which does same thing.

Louise - may have to invest in the autofocuser at some point too.

Thanks all.

Darren

Thanks guys for the tips. Defo gonna get a bahtinov mask as that seems the easy fix.

Happy-Kat - I don't have android but I can use the live view software from canon on the laptop which does same thing.

Louise - may have to invest in the autofocuser at some point too.

Thanks all.

Darren

Edited by Dazzyt66
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Looks like everything that I was going to suggest has been covered here already.

Batinov mask

live view and zooming trick

focussing on a star 1/3 from the center.

use an electric focusser if you can - it'll help stop vibrations.

The putting the ISO up to max is a great trick, I'll have to remember that one for next time I'm out.

Also you don't need to focus on the object itself.  Just find a bright star nearby and focus on that.   By nearby, I mean somewhere in the same region of the sky.  i.e. don't focus on a star near the zenith, then take a picture of an object near the horizon.  The reason is that the amount of atmosphere is different and so the refective index of the sky changes - basically it changes the focal point when you slew the scope.

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  • 4 weeks later...
On 17/01/2016 at 10:12, happy-kat said:

The best thing I have found is using my 7 inch android tablet running dslr controller connected direct to the 1100d using and otg cable into the canon USB cable into the camera. Can control the camera totally and focus easy as what camera sees is shown on the tablet and can zoom in on a point x5 and x10.

Imagine the image with a line a third in from each edge. Where the lines intersect on a corner is a good place to find a star to focus on.

This sounds very interesting as I have a Tesco Hudl android tablet.  I'm a bit dim today ... sorry ... but how exactly do you connect the tablet to the camera (which in my case is a Canon 1000D).  What does otg stand for?

Many thanks

Pete

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out of curiosity have you tried backyard canon? (think you can download a free trial) I use the nikon version so when I focus its on the laptop screen and theres a few tools that help you to get focus, I always use the FWHF (something like that) and all you do is turn the focus untill the numbers get as low as possible (around 3 ish) once you have done that its focused. 

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Android application DSLR controller

Camera (old cameras like canon 350d are too old to work)

Otg cable (stands for "on the go') costs about £4.

Usb cable that came with camera.

Plug USB camera into camera. Plug otg cable on that. Plug otg cagle on android device. DSLR controller app can be launched.

Note before buying that app install their free shutter release app,  if when using that you can fire the camera shutter you know the full app will work.

 

gallery_28282_2962_479727.jpg

 

Edited by happy-kat
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1 hour ago, stargazerlily said:

This sounds very interesting as I have a Tesco Hudl android tablet.  I'm a bit dim today ... sorry ... but how exactly do you connect the tablet to the camera (which in my case is a Canon 1000D).  What does otg stand for?

Many thanks

Pete

OTG = On The Go. It is a type of connector that connects to the Hudl's mini-usb socket and provides a proper female USB socket for a normal USB cable to plug into.  It performs some form of protocol change too.  I got mine (I have a Hudl too) from Amazon for about £5.

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34 minutes ago, stargazerlily said:

Many thanks happy-kat and DorsetBlue.  

I already have a OTG cable ... just didn't know it was called that :)  Next step ... download the DSLR controller.  

Cheers

Pete

Just a little warning, I went to use it last night and I couldn't get DSLR Dashboard to zoom in during Live View (which made it pointless).  Might have to contact the author, but it could be a limitation with the Nikon D5000.  DSLR Controller is Canon only.

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First install chainfire's remote release application  if that works with your camera then get the full application.

Edit: just off the read about nikon support in dslr controller

Edit: oh no go for Nikon, as Canon only.

Edited by happy-kat
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An update ... just installed DSLR Controller on my Tesco Hudl (running Android 4.2.2).  I have successfully used the App to take a few test photos using my Canon 1000D.  I could see the image on the Hudl as Live View was enabled on the camera.  Next test will be for real ... out doors pointing at the sky :)

Pete

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39 minutes ago, happy-kat said:

Using my 1100d I do not need to be in live view on the camera for the image to show on the tablet. You don't want live view on if you can help it as it will make the sensor hot

Yep, best to use it only for short periods. And before you start your imaging run, give the camera a few minutes to cool down again.

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Thanks Happy-kat and Uranium235 for the heads up about using Live View.  My aim was to use the Live View feature to help get a good focus.  From my brief test this morning it appears to be much easier to use the magnification options on DSLR Controllor to help get a good focus rather than on the camera itself.  Also, the Tablet has a larger viewing area :)  

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If the camera is in manual mode (it should be) then you have a lovely big screen to change all settings from. I like to leave the lens in manual focus and find focus by hand using the help of the nice big tablet screen. Ideally pick a star a third in from the edges on a corner intersection and focus on that.

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On 12/02/2016 at 14:45, happy-kat said:

If the camera is in manual mode (it should be) then you have a lovely big screen to change all settings from. I like to leave the lens in manual focus and find focus by hand using the help of the nice big tablet screen. Ideally pick a star a third in from the edges on a corner intersection and focus on that.

Great tip about the one third distance, thank you.  Would you advise switching on the grid on the Tablet display?

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