Compare Apogee & Perigee Moon sizes here...

http://apod.nasa.gov/apod/ap071025.html

and Libration or lunar wobble during 1 month here ...

http://apod.nasa.gov/apod/ap051113.html

Mike

Hi Roger

Nothing taken with the K5 & scope yet but hope to do so before Orion slips away for another season.

Just trying to get to grips with the K5 limitations using the 18-135mm lens before going up the focal length.

Mike

Hello Roger

Really nice images.

I think you probably struck the best compromise ISO versus exposure time...always compromises.

The only way to record more stars while lowering your ISO is to increase exposure time slightly by mounting your camera on an astronimical motor drive of some description ...but the compromise ...well you house & trees would suffer motion blur.

In the good old days of film your fixed camera exposure could have ran another 5 to 10 secs without showing too much trailing as the star were hidden within the bloated halated star image but because DSLR sensors resolve so much better than film there is no room for error.

To record the red colour (hydrogen wavelength) in the Orion nebula a DSLR sensor needs to be modfied which is better done with an old inferior camera like a Canon 450D than a K7 as the process is not reversible

Unfortunately Canon are the only manufacturer supported by astronomical filter manufacturers because relatively few have used Pentax & Nikon for astronomical photography.

Mike

Really great result there Bob and my hat goes off to those that try this with a DSLR.

The only problem I have with taking long star trail images using a DSLR is the thought of that wear & tear on the camera electronics and all that post processing just to produce star trails still done better & more simply with film.

DSLR's certainly do a fine job on such shots so long as the sky background is not completely dark such as at dusk. However from dark sky sites where the sky background is much darker because each exposure is quite short to avoid sensor noise the sky background doesn't record so well and as a result the latitude between the bright stars and background causes harsh contrasty startrails with very dark backgrounds not aesthetically pleasing.

A single film image on the other hand not only records the star trails of any length you require depending on the ASA & chosen aperture but also the background glow of the milkyway.

DSLR's can record the milkyway very well ...and not too bad for star trails (with a lot of work) but to capture both milkyway & star trails in camera while being aesthetically pleasing is near impossible.

Mike

Could always buy her an ironing board as compensation ...it's worked on this forum before.

Mike

Afraid you were going to say that.

Oh well ...I may have to eat my words, the streaks do appear to brighter at one edge fading off across the frame, while the streaks seem mostly parallel the broader centre band appears off ...very strange.

Guess it's a process of elimination to exclude reflections as the cause first. It may well be a fault, I have not seen anything similar in mine and it has had quite a few very testing exposures.

Hope you get to the bottom the problem soon!

Mike

I'm thinking the same as Yves on this one.

Looks like possible streaking caused by uneven application of cleaning fluid. The lines are not dead straight and are along the length of the sensor which would be the natural direction to clean rather than across the short way indicating human input. Light scatter on the sensor surface could be polarising along the streaks splitting white light at the purple wavelength just like in a rainbow.

Suggest checking your sensor again with loupe magnifier while shining a torch in at an oblique angle and see if any streaks are noticeable, failing that another wet but even application of the sensor might be needed. Perhaps your sensor cleaning swabs are a little too narrow which could be leading to an overlap streak pattern, a slightly wider swab may be required.

The only issue I have seen with heating in a DSLR sensor manifests itself as 'amp glow' ...a brightening in dark images at one of the short sides of a frame. I have fired off quite a few exposures 30sec to 300sec with my K5 with no sign of problems, in fact surprised how little amp glow is apparent compared to my wifes Canon 20D so unlikely to be a heating issue.

Mike

Received my £120 cashback today (27.01.11)


Oh dear ...shame to have that cash burning a hole in my bank account.


Mike

Great images, the glass looks in superb condition too plus do I see a filter compartment just in front of the aperture ring .....mmm very nice indeed!

Mike

Considering the growing popularity of using telescopes & spotting scopes with DSLR's for astronomical & long focal length wildlife photography perhaps there is an opening for another category, there is after all a category for everyones excellent 'Macro' images ...'Specialist' seems to be the only other option to post in at the moment plus the opposite extreme in focal lengths would create a nice balance.

We could still use Specialist or Landscape for the wide field related subjects.

Would suggest category... Telescope/Spotting Scope/Telephoto

Mike