Stub Mandrel

Those sort of tables need Danish Oil every year. Forget one year and they've had it... I know!

Another one salvaged from the grot. Luckily there was a rectangle virtually without dust. Stacking in AS!2 and Registax then combining both roughly 50/50 seems to have eliminated all the noise.

The signal from the CCD/CMOS has to be processed to perform the A2D conversion. ISO affects the gain applied during that conversion and as it can't be zero gain then EVERY digital image has to have some effective ISO rating

I've read that with my Canon D450 and long exposures the lowest read noise is at 800 iso, and taht iso 1600 isn't significantly worse. Try it and see.

An anyone answer me a question - is the histogram x-scale linear or logarithmic scale? i.e. if it has say 5 divisions are these: 1 2 3 4 5 - linear 1 10 100 1000 10000 - log base 10 1 2 4 8 16 - log base 2 My guess is that it's a log base 2, which would fit with things like changing aperture by one f-stop, changing ISO by one step or doubling exposure would move the histogram by one division, this would also explain why a histogram shifted right by a longer exposure doesn't get noticeably wider. Does anyone know what scale Canon use?

Here's my first whole disc image, shows how accurate Cotterless's sketch is!

I'm not convinced. Why? because the gradients on my images are sometimes caused by vignetting (not entirely eliminated by flats) combined with light pollution and sometimes nearby bright stars and the moon so they can be quite complex - and they change over time with an EQ mount as stars typically move out of the LP in my bit of sky. This means very complex patterns. Removal programs don't seem to struggle with the resulting effects though. So, although I agree with your point that rotation means anon-linear gradient, in practice I think its only a problem if you use a gradient based removal strategy.

50% of users click 'I'm not sure' the other 50% are liars :-)

Just went out for a bit, came back and DEC had gone to pot so a minute-by minute version is not likely! Will put the Barlow on again when it gets near the spot. By gum my sensor is dusty :-(

Miraculous! Excellent seeing here today - and Mercury is on the disc! The spot is showing a nice surrounding dark zone too, even in live view. Sorry folks with cloud.

Ha! the Sun's out in Burton! It's going to be cloud -dodging

I have to make a dark box for the laptop. I use the DSLR with my workshop coat over my head, but my attempt to see my laptop in full sunlight for video was farcial.

Here's a rather belated update. I've discovered two issues with my current setup: When pointing high I get double and mis-shapen stars. i think this is a combination of backlash in DEC and the fact that the out-of balance I use to combat this becomes negligible. I will try and reduce the backlash and try using a bungee or some other way of 'preloading' the DEC axis. My RA stepper had a jerky movement. this has been solved. As a test of the improved stepping I made a single 2-minute sub after focusing on Arcturus the other evening as an experiment. This was with a relatively light setup, but subs taken later with the 150PL at 60 seconds were clearly much 'tighter'. Obviously this sub was over-exposed and it has only been stretched and colour corrected, but I think it shows that the EQ3-2 can do reasonable sub lengths given my LP-cursed skies.

This is what Astrometry.net says:

It's interesting that my 76mm tele lens doesn't seem to suffer bad CA (there is a little bit). It has a rather different lens setup to a scope, with a set of supplementary lenses inside (I suspect these are a mild barlow that extends the FL of the objective from 300mm to 400).

there are hints of the Pelican in the North America shot. Is your camera astro-modded?

You prompted me to have another look at Startools. I think a solarise filter would have had a similar effect. A visual car-crash. I think the problem is that each step is carefully explained in terms that are understandable only by someone who knows how to work the program already.

Unless its the 6" scope, I take flats with the camera and lens/scope at 0, 90, 180 and 270 degrees. I have a patch of diffusely illuminated plain wallpaper that does the job really well. The big scope seems to give good results from a patch of early morning sky, well away from sun or horizon.

With my gear, it's flats that make the difference.

This thread inspires me a lot. Although I have an EQ mount, it's only an EQ3 and without guiding sub-lengths are limited. The message is clear stop eating my heart about about not getting 2-minute subs and take lots of 1-minute ones knowing that nearly all will be usable.

Much nicer! More detail in the nebula.

Nigel G & the Admiral If you have a photo-editing package with 'gamma' try reducing it to about 0.82 to 0.90 (unadjusted setting is 1.00). It will darken the background and increase the contrast in the galaxy, without losing you any detail (as long as you don't over do it). If you have photoshop, use the levels histogram and don't tough the end sliders, just the middle one. Gamma is a very simple tool and is fantastic for improving details in shadows or burnt out areas of ordinary photos.

Fantastic piece of work, Damian. It looks totally professional and most of all it doesn't have an 'over-engineered' appearance. Next? 26" mirror on an EQ mount?

Very nice, something on my 'bucket list' which is many times longer than the number of clear nights! I think you can use the button marked 'Insert other media' to put a gallery image into a post.

:-) Those pictures are quite hard to understand as my brain doesn't 'see' the mirror!