Uranium235

On 26/08/2019 at 20:11, matt_baker said:

Last Tuesday, I managed to go out and image M13 just fine, with only a couple of stars in one corner being elongated due to my focuser tilt.

Last night however, I was trying to image the Iris nebula and the stars looked awful.

I made sure to collimate and make sure the focuser screws were tightened nicely. Although I did push the mirror up slightly with the collimation screws to try and minimize the drawtube obstruction.

Collimation was done with a cheshire eyepiece and collimation cap.

My focus was also good from my bhatinov mask.

I think I know it's not caused by differential flexure, since the stars look awful even from a 5 second exposure which I've uploaded for all to see.

Could anyone help me out?

If you look closely at the corners, it will tell a story. The left side has normal coma (I assume youre using a corrector?), while the right  is a different type of distortion (radial).

That would indicate some tilt, either in the focuser, the way the corrector sits in the drawtube, or whether you have any loose connections. You might need to take time to square your focuser, simply tightening up all the screws doesnt quite mean that its pointing at the right spot on the tube wall.  You have to remove the secondary and put in a marker for where the focuser tube should be pointing. There is stuff on youtube how how to do this, but I wouldnt attempt it until you have the bits required (digital calipers etc..)

The stars in the middle are a bit so-so, but you didnt state whether you were guiding or not.

Its been a very long time.... perhaps too long..lol.

20x450 Ha on the Veil, starting off on something easy. No calibration either. I'll probably process it again later on when I remember what it is I used to do

6 hours ago, Adam J said:

whats your thoughts on reducing that to t2 thread straight after the M48 thread? would that result in vignetting?

If the FW is attached directly to the camera - the m48-T2 adaptor will be about 11mm. 

If you have a large format camera (diagonal of 22mm +l, I would use 36mm or 2 inch filters anyway. 

The shorter I make the mod, the more options the user has got to configure it in a way that suits their camera. ☺

9 hours ago, Space Oddities said:

Rob, I'm curious about the impact of your modification on the flange distance of the lens? Is it going to be similar to the Canon bayonet?

I'm trying to keep it as close to the original distance of 44mm. But I can afford it to be up to 2-3 mm thicker (still leaves loads of room for a FW).

I'm making the m48 thread just 4 or 5 mm.  That way any extension ring or FW will screw right up against the lens mod if you so wish ☺ 

Still waiting for the lens... ughh this is like pulling teeth...lol 

Still waiting for me lens! Looks like it's going to be a drop ship jobbie, so perhaps Wednesday or Thursday.

Well.... this is turning out to be a popular idea

Ive tried the Geoptik adaptor, but i found it a PITA to change filters. The adaptor I have planned will allow the useage of pretty much any standard thickness FW (~21mm), as long as your camera backfocus requirement isnt ridiculous (like 20mm+).

1 minute ago, KyleStoke said:

Yeah didn't really mean it as a direct example more just a view of the inner workings, there isn't much in there. Seems to be as simple as 3 screws.

I'm with you on the screw fits, I'm currently suffering from a horrible amount of tilt in my system  

Its alright Ive already seen the inner workings - a fellow SGL member was brave enough to take his apart so I could see if there are any nasty surprises lurking underneath the bayonet, and there isnt - so its all systems go

37 minutes ago, KyleStoke said:

Hi Uranium, I am also very interested in these. 

Take a look at this, I don't want to put the mockers on anything but seems very straightforward once you have a suitable replacement mount.

https://www.dpreview.com/forums/thread/4234335

https://www.dpreview.com/forums/thread/4157183 

This also opens up the possibility of getting any version of the lens and simply replacing the mount (unless I've missed something)

Im aware that the same rule will apply to any variant of the 135mm (and maybe other lenses - even for mirrorless), the modification Im proposing is about getting completely away from bayonet connections and moving it to a screw-fit.

Those links seem to deal with the idea of switching between lens mounts of various manufacturers, which doesnt really apply to what im doing as im ordering a custom mount (focused on AP) from scratch. Of course, once its modded you wont be able to just pop it on your DSLR again - unless you take 10min to swap out the lens mount

Lets concentrate on the 135mm f2 MF for now, get it working - and then we can take a look at where else this can be applied.

If the camera is modded (as in filters removed, but not replaced), the sensor may need to be re-shimmed to work properly with some lenses. I had to do it to avoid the hard infininity stop with the Samyang 135mm.

Or, you can try using EOS utils to get a proper look at stars while focusing.

Typically, a modded camera in my experience has a difference between what you see through the viewfinder, and what you see on the preview screen  - the preview screen is the one that tells the truth (for daytime photography anyway).

1 hour ago, Adam J said:

I am most likely getting one of these so hold one for me please. 🙂

PM sent

7 hours ago, Adam J said:

Sounds like something lots of people would find very useful. 

Yep indeed if the modification works, Im going to order a bunch of them to be machined, but I have to run it past admin first.

Not sure where I will stand on intellecual property rights though  

46 minutes ago, Adam J said:

All, 

I will be going to Aus for a month early next year and am thinking of one of these for portable work with my ASI1600mm pro.

I see a large number of people supporting both the lens and the camera as opposed to clamping only the lens or only the camera to the mount, is this strictly required or are people just doing it because droop / flex is an issue with the canon connector?

Adam

Adam, Im currently working on a fix to completely eliminate the droop issue with the EOS bayonet connection (conversion of the lens to M48 thread). Its going to be a prototype so watch this space and I will have some news in a week or two.

Currently, the lens needs to be supported because its quite heavy, which causes compression of the bayonet fitting as the mount slews about - its only secured with three springs, which isnt really strong enough when imagng at f2 tbh - which is why people are supporting the lens to minimise the movement. Moving to an all-threaded connection will (in theory) resolve that issue.

Another bonus of going all threaded is that you will claw back the space taken up by the EOS-T2 adaptor.

Looks like im back in the Samyang club ordered a new 135mm today (should get it next week).

Excellent.......

Team scumbag at the ready! 

2 hours ago, Adreneline said:

65.00mm

48.33mm

43.53mm

 

Awesome ☺ thanks! 

Just a thought..... if im to attempt modding the 135 I will need three measurements (I cant do it myself since I dont currently own a 135). The rear aperture looks quite wide when compared to some M42 lenses, so I need to know exactly what it is before hunting around for an M42 donor lens. If someone could whip out a digital caliper or ruler (for a rough measurement) that would be handy  

The three measurements I need are as follows:

If I cant find a lens that is suitable, then I know a chap who just might be able to machine something. If I were to go down the custom route, it would probably end up being M48 instead.

14 hours ago, Alien 13 said:

I found that most old M42 lenses had a back that had three screws too, I did swap out a old lens using a donor one that fitted with no mods so worth taking some measurements and a visit to a few charity shops.....

Alan

Sounds like a plan! I've got a bench drill so I could drill any additional holes that might be required. The M42 donor lens doesnt even have to be working, as im taking it apart for bits.

Edit: Patent pending....lol

Looking at the rear end of a Sammy, it looks like the bayonet can be removed (held on by three screws). It might be possible to engineer something to replace it, but it would need to be precision stuff, not something I could knock up on the kitchen table.

12 minutes ago, Alien 13 said:

Sounds good, as to price a similar Canon version would be 6K+ so its a bargain......

Alan

Hmmmm.    that PL thingy has got me thinking a bit. It would be so nuch better if there was a custom adaptor that did away with the whole bayonet business  for standard photo lenses, it would hex bolt to the lens (using compression) and be ultra short....lol... I know might be dffiicult to envisage, but given some time and perhaps a test 3d print (before moving on to aluminium), it might be possible.

lol... I wish Samywang made an M48 or T2 fit version... that would be fantastic

I was looking around for a cheap used 135mm sammy, but came across something very interesting this evening. Samyang have released a 135mm cine lens, rated at T2.2 (transmission value, rather than F ratio). Its expensive, but I found that you can get a variant with a fitting  called "Positive Lock". Which gives a much more secure fit than the standard EF springs found on your typical camera mount (as cine lenses are heavy beasts).

A little more digging found that there is a PL - T2 adaptor available, and the flange-chip distance of the lens is a generous 52mm.

Would be nice to see someone with deep pockets give that a go for astro but as always, best to keep your powder dry until someone else makes the leap. Its only been released this month, so its yet to get any attention. If its anything like the standard 135, it would be quite special - especially given the secure nature of its mountings.

The price? £1544 .... hahahaha yea right (if I won the lotto)  

Weight? 1.4kg .... lol...

Thats a lot of dough for 135mm (though probably cheap in the world of cine)

https://rokinon.com/xeen/xeen-cine-system/135mm-t22

It is entirely possible to get rho ophiuchi from the UK 😊 you just need a dark, unobstructed location, and pick your nights well (no fuzzy skies). 

Now is a good time for it.  But you have to stay up well late for it...lol 

Actually, I'm thinking of getting yet another of these lenses since my new home has such a limited window of opportunity I would need to cram in as much data as possible in just 3 hours... and the only way to do that is to go superfast.

On 20/06/2019 at 16:53, Kaydubbed said:

At F2 would you get phase shifting issues using normal narrowband filters?

It also depends on the bandwidth of the filter.  A standard Baader 7nm filter is fine in my experience, however a 3nm Astrodon would be more inefficient. A 12nm Astronomik on the other hand would fare better.

But hey, youre at f2!!   so a slight loss in transmission is no big deal at that speed.

There ya go... M87 jet from the 130:

Crop

On 13/05/2019 at 08:03, JohnSadlerAstro said:

Hi,

It's something I definitely wasn't expecting! The jet is in the correct direction though, and is in the opposite direction to the coma. It's also strongly luminous in the blue.

I would suggest disregarding the standard method of taking short (<1min) subs, my ones were 120 and 200 sec, at iso800, I believe. It's quite possible to get the galaxy core + jet without too much clipping. 

Good luck!

John

Just working on it now mate (its been a while since I last got out).

But.... ive just checked the first sub (240s) and bingo... its there!! my first (intentional) jet!

I'll leave the camera running for an hour or two - just for the sake of nose reduction - and hoovering up some background fuzzies. Im getting a few unexpected bumps in RA guiding though, no idea why becuase there is absolutely no wind our there tonight.