Alien 13

25 minutes ago, vlaiv said:

Thinks to keep in mind when considering type of monitor and calibration of it:

1. If you want accurate color in your astrophotos - it has nothing to do with monitor / calibration of that monitor. Colors of light coming from objects out there is independent of what hardware you have or how you calibrate it.

2. If you want to accurately reproduce color from your astro photos - you need to accurately record them (do color calibration of your data and use known color profile - either sRGB or some other together with ICC profile), and you need accurately calibrated monitor - see video above.

3. If you do creative work and in that process select a certain color and want other to know exact color you've selected - then you need accurately calibrated monitor and all other things (profile with your image and those looking at your color to have calibrated monitor).

First point is reassuring - you can produce accurate astro photos even if you don't have high end monitor or great calibration. Point two is incentive to get one of those calibration devices and good monitor - if you want to look at colors of objects as they are.

I use my laptop screen (calibrated with a spyder) to do all my photography and astro work, now a laptop screen has a very limited gamut but what calibration does and is the the critical thing with any photo processing is to set an accurate white and black point and of course good stable transition between the two with a smooth greyscale rendition.  

Alan

8 hours ago, Midnight_lightning said:

I'm completely new to this topic, as you may have guessed. My monitor comes with Eizo's ColourNavigator software - am I right in thinking that using this with the Spyder will do the calibration? 

The Spyder and many others of a similar type of calibrator fully automates the whole calibration process by outputting various levels of R G B and taking measurements of them but does not have the ability to change the monitors internal settings. The result is a dedicated profile for your PC/Monitor combination. The software will set up some basic starting points that you will have to set on your monitor manually to ensure that any profile used by your graphics card wont overdrive it.

Proper monitor hardware calibration is usually a manual affair unless the manufacturer makes a dedicated calibrator for it but you can get reasonably decent results by using a phone and app.

Alan

I would like to add a small note regarding Monitor calibration using devices like the Spyder, I have the Spyder 5 pro and what it does is create a custom colour profile for your graphics card but does not in fact calibrate the Monitor itself.

Alan

5 hours ago, hawksquawks said:

Okay I have been out and tested the scope I took a photo with my DSLR, the chromatic aberration is very bad in photos but not bad at all using an eyepiece can this be explained?

Even a std DSLR will have much more sensitivity to the extreme red and violet ends of the spectrum compared to the human eye so this might explain this CA.

Alan

I do wonder if projects like star link dont in fact increase the interest in astronomy massively, I myself much prefer transient object like SN/Meteors etc.

Alan

12 minutes ago, JamesF said:

It certainly will be interesting to see the calculations when you've done them, Magnus.

James

+1 to that..

Alan

3 minutes ago, JamesF said:

I assume it applies to Maks as well though given the difference in design it may not hold, but there is occasional discussion that (for example) Celestron SCTs are designed to give the best corrected image at their quoted focal length.  There may perhaps be a trade-off between correction and field of view (like there's ever not a trade-off where telescopes are concerned

James

I expect the manufacturers of Maks and SCTs optimize the performance for use with the std diagonal and eyepiece spacing but then add a T2 thread on the visual back so maybe they have optimized for both visual and imaging at differing points.

Alan

39 minutes ago, SimonWhitfield said:

Now, the white focus line on mine is the other side of the 10m mark when attached to the QHY183M and filter wheel and focused on the windmill 2.5km away... but bang on where it is supposed to be when I connect it to the Canon.

 

Simon

 

The sensor on the Canon 6D will have been shimmed to minute tolerances so that is your benchmark, as Adrian has said you need to add whatever spacers are necessary to match that with the QHY camera.

Alan

I have played around with spacing but have never convinced myself as to which is best so in general I try to put my DSLR sensor at the same point as that obtained with a diagonal/eyepiece combination. I would like to know though what is likely to be the best distance to minimize any vignetting..

Initial thoughts are greater spacing=longer focal length=shallower light cone=less vignetting caused by the focus tube but then the longer focal length may cause issues because the secondary might not get fully illuminated.

Alan

1 minute ago, SimonWhitfield said:

Hmm, hadn't considered the sensor window. I've got another 10.5mm of mixed spacers I could throw into the mix, and it looks like it would take that much to get the infinity mark anywhere near the focus mark but that would just be silly, surely? From 44mm to 55mm?

Tonight looks like it might just be clear enough to run off a few test images, just to see how the stars look. I guess that's the ultimate test, regardless of anything else...

 

Simon

I agree Simon, a star test will show if the spacing is critical or not..

Alan

5 minutes ago, SimonWhitfield said:

I have used a digital vernier and it all seems right, even measured the individual bits to make sure they were accurate. I even used the calculator on my phone to add the individual millimetre measurements together, just in case I was having a brain-fart 😆 

I agree about the Canon... that should be the reference point. This is just weird...  

It certainly is strange, from memory every bit of glass in the optical train adds on average 1mm to the required backfocus distance so 1mm for the filter and 1mm for the sensor window. It could be interesting to see how much extra spacing is required to get the focus mark in the correct place..

Alan

2 minutes ago, SimonWhitfield said:

I did add an extra 1mm, which I think was over-doing it as the Baader filters are 2mm thick, but I also tried with an extra 0.5mm.  The only difference either seemed to make was to move the focus point slightly closer to infinity, but I still have 60 degrees of rotation before I get close to the infinity mark. 

Simon

I admit that its very odd but still think the infinity mark on the lens is telling the truth as shown when connected to the Canon camera.

Have you tried measuring the overall spacing with a vernier?

Alan

It does sound as if your spacing is a little short, did you allow extra for the filters?

It depends how the focusing is done on this lens, some lenses move the whole assembly and others certain elements only, if its the former then it wont matter at all where the focus position is but might do with the latter.

Alan

I use one of these dovetail bars in conjunction with a ball head on my EQ3-2 for my DSLR.. The ball head lets you choose the orientation of the camera and hence the composition.  

Alan

I have the 70-200 f/4L and its fine for AP even wide open plus you can use it with some teleconvertors if you want a longer FL, the reports I have seen on the 200mm prime suggests it needs stopping down to f/4 for AP so has no real advantage.

Alan

I had the 18-55mm IS lens and it was fine, a pain to focus with its sloppy focus ring but provided you picked a feint star away from the center to get focus then it could be used wide open, it performed far better than my nifty fity which still struggled even when set at f/8.

Alan

Just now, Davey-T said:

We did didn't we before hard drives we had floppies A and B

Dave

Correct, I had forgotten about the floppies, the 5 1/4 was realy floppy and did play with some even bigger ones.

Alan

2 hours ago, Chaz2b said:

Win7 declared the partition as drive D, so I’m puzzled if you say it should be allocated to an external drive.

chaz

It was normal in the old days to have a single hard drive and CD/DVD drive that usually got allocated as drive D. I often wonder why we never had A and B drives..

Alan

2 minutes ago, Chaz2b said:

Right! I’ve downloaded UNetbootin, and Linux mint xfce, opened up the install page, asks which drive to install to, I have C and D, c has win 7, d is unused so I want to install to that drive( partition) but it doesn’t show D! Why not?

do I continue to install into C and the move it to D?

chaz

Drive D is usually allocated to an external type drive, I installed mint on my win 7 laptop keeping it as a dual boot machine but created a partition on the C drive for that purpose.

Alan

17 minutes ago, saac said:

Or the inertial dampener, or environmental control, or the lights , and what about stirring the oxygen tanks - wait that was Apollo 13     Of course there is the old question as to why when two ships meet in space are they always the right way up to each other ?   Ach we are spoiling the escapism!   I must admit I did enjoy the new Amazon series well worth it if you have yet to see it.

Jim 

I used to love the way the junior officers took over the "night shift" on Voyager as though expecting that the whole Galaxy was asleep...

Alan 

2 minutes ago, JamesF said:

If I gently put the most convex and concave faces together then there's a definite vacuum when I try to separate them, so I reckon they must go together.  There's also a thin plastic spacer that is bent on one side as if it were caught around the edge of the inner lens, so perhaps that's the cause of the problem.

The cell is plastic and possibly not entirely round, so I'll see how reassembly goes...

James

The spacer is there to prevent any direct glass to glass contact, have made suitable spacers from various things like coke cans/milk cartons in the past but that damage you mention is probably the main culprit.

Alan

16 minutes ago, JamesF said:

Well, the current arrangement appears to be less curvy, curvy, inverse curvy, flat-ish.  Judging by the dirt on the inside lens faces someone has definitely had it apart in the past (I bought it used).

James

Usually the inner two surfaces of the lens elements match each other in curvature, if they are dirty might as well clean them and try reversing the front element but make sure this doesn't cause any glass to glass contact. The flattish surface should point towards the eyepiece end of the scope like this.

Alan

4 minutes ago, michael8554 said:

I can't wait for the opportunity to slip that into the conversation at the Royal Institute........

Might first be worth holding the scope vertically by the focuser end, and giving the front a gentle bump on a carpeted floor - might just be the elements need joggling into the correct positions, since the coma is in one direction.

Michael

That might work, Achros do usually have a bit of free play in the lens cell to avoid pinching effects.

Alan

7 minutes ago, JamesF said:

And more to the point, can it be fixed and how?

It looks a lot like coma to me, but in a refractor? (600mm fl f/7.5 achro).

James

Looks like someones had the lenses out and put them back in the wrong order, curvy less curvy inverse curvy flatish is the normal configuration I think.

Alan

I have no doubts that the only Aliens that had the technology to send radio signals and have the ability for space travel would look pretty much like us....

Alan