K20D Live view usable for astrophotography ?

[glasbak]

dear K20D owners,

at the moment I see only one reason to upgrade to a K20D,
and that is the ability to acurately focus with liveview on the nightsky.
So, has anybody tried this ?
Or is the live view not sensitive enough to focus on a moderately bright star ?

And, does the CMOS sensor also have a hot spot (corner) when doing long time exposures like the SONY CCD's ?

George

 

[justin23]

I'm not quite sure what you are asking here.....
firstly you can't manually focus with live view. it goes black while it AF.

Secondly a star would be closer to infinity than many other things we photograph with focus at infinity.

The CMOS sensor however uses less power and apparently stays cooler than a CCD sostar trails will be less prone to heat generated noise, i'd have thought. I may test this during the week.

dear K20D owners,

at the moment I see only one reason to upgrade to a K20D,
and that is the ability to acurately focus with liveview on the
nightsky.
So, has anybody tried this ?
Or is the live view not sensitive enough to focus on a moderately
bright star ?
And, does the CMOS sensor also have a hot spot (corner) when doing
long time exposures like the SONY CCD's ?

George

--
Justin
--------------------------------------------------------
The Blind Pig
http://www.jeber.com/Members/Justin/Gallery/
Photobucket
http://s107.photobucket.com/albums/m313/justin-23/

 

[glasbak]

I'm not quite sure what you are asking here.....
firstly you can't manually focus with live view. it goes black while
it AF.

Accurately focus is not achieved by using auto focus, and on the night sky AF won't work at all.

So I am speaking about manual focusing while viewing the (magnified) live view screen with the camera attached to a long lens/telescope.

Secondly a star would be closer to infinity than many other things we
photograph with focus at infinity.

Modern lenses focus beyond infinity for auto focus control (and other) reasons, so putting a AF lens on the infinity mark is very inaccurate.

George

 

[Cideway]

I just tested it, i found the brightest star pre focused with the VF and then turned on LV and there was able to fine tune my focus.
--
Some people's photography would be so much better if they left the lens cap on.

If you focus on the pixels you loose the image.

GMT +9.5

Pentax SLR talk FAQ
http://forums.dpreview.com/forums/read.asp?forum=1036&message=23161072

 

[justin23]

OK well i just tested live view. you can manually focus with it.
Not sure about how easy it would be with stars.

I know what you mean about lenses going past infinity, I found with shots of mars and venus that is the case.

--
Justin
--------------------------------------------------------
The Blind Pig
http://www.jeber.com/Members/Justin/Gallery/
Photobucket
http://s107.photobucket.com/albums/m313/justin-23/

 

[snostorm]

Hi George,

As has been noted, you can manual focus with LV. Another point that might be helpful is that LV works with video out, so you can use a remote TV to focus with, if that might help in some situations. You can even use a VCR before the TV to record video if you wanted. I don't know if this would be of any value to your use, but I thought it could be relevant.

Scott

 

[glasbak]

I just tested it, i found the brightest star pre focused with the VF
and then turned on LV and there was able to fine tune my focus.

Do you know which star, and the effective lens diameter (not aperture)?

george

 

[glasbak]

As has been noted, you can manual focus with LV. Another point that
might be helpful is that LV works with video out, so you can use a
remote TV to focus with, if that might help in some situations.

Interresting, does this liveview also makes possible that you can get a viewfinder image in the remote assistant ?

george

 

[Cideway]

It was straight above me, and blue, i'm in the southern Hemisphere the lens used was a DA* 50-135 at 135 f2.8, i was testing hand held
--
Some people's photography would be so much better if they left the lens cap on.

If you focus on the pixels you loose the image.

GMT +9.5

Pentax SLR talk FAQ
http://forums.dpreview.com/forums/read.asp?forum=1036&message=23161072

 

[glasbak]

It was straight above me, and blue, i'm in the southern Hemisphere
the lens used was a DA* 50-135 at 135 f2.8, i was testing hand held

Thanks,

that must have been Sirius, magnitude -1, with 50mm diameter lens, so it should also work with magnitude 2 stars behind my 150mm diameter telescope.

Unfortunately, magntude 2 is still quite rare in the field of view of my telescope.

George

 

[Russell Evans]

As has been noted, you can manual focus with LV. Another point that
might be helpful is that LV works with video out, so you can use a
remote TV to focus with, if that might help in some situations.

Interresting, does this liveview also makes possible that you can get
a viewfinder image in the remote assistant ?

I've asked this a few times and the answer as been no so far.

Thank you
Russell

 

[justin23]

I focussed on mars last night with live view at x8 magnification. clearly red and round in my LCD screen

Shame my photos were not that great. there must be a trick to photographing planets. I worked out underexposing is required, because like the moon they reflect the suns light.

--
Justin
--------------------------------------------------------
The Blind Pig
http://www.jeber.com/Members/Justin/Gallery/
Photobucket
http://s107.photobucket.com/albums/m313/justin-23/