SW 150PDS light leaks

[lensman57]

Hi,

Just in case anyone is imaging using a 150PDS or anyother SW NEWT, I had noticed some strange gradients on my captures that I could not easily get rid of. I traced this to the light leaks from the rear mirror cell of the 150PDS and I am sure of this. One evening while leaving the camera to take darks indoors,  the background value of the darks showed an increasing level as the early hours of mornning  approached and the sky got lighter, now I have resorted to wrapping a black binbag around the rear of the scope untill a more satisfactory solution could be found. I may take the cell out and have a look at this at some stage. If this is a design fault then with regret these scopes are not fit for purpose but it is a little too late to do anything about this.

Regards,

A.G

[dobbie]

Hi lensman , yes your right I found the same on my 200 PDS , when you take the cover off the front put it on the mirror end and a bit of black tape around to secure it, problem solved

[Skyline]

got my wife to make a cap with an elastic fit, so I can fit it around the 130P DS.

Al.

[Cornelius Varley]

I don't think it is a design fault as such, the rear cell of a newtonian is usually open so as to allow free movement of air to allow the mirror to cool. Something like a black plastic bag sounds like a good idea. The SW reflectors I've owned had a loose fitting plastic disc between the rear cell and tube.

[Thalestris24]

Hi

Funnily enough I noticed this the other day when testing out the new Ascom driver for my qhy8l. I was taking sets of darks during the day and was dismayed to find that long exposure darks weren't! I put black bags and even foil over the front end - over the endcap. There was still some light leakage so decided the mirror end needed covering too. I was also stretching the darks looking for signs of amp glow and was surprised to find I could stretch them to white. Never tried it before and had assumed that if an image was totally dark that it couldn't be stretched. Of course, I'd forgotten the bias noise would still be there! This realisation prevented me from becoming paranoid about light leaks - I think!

Louise

[Steve Ward]

Are you sure it's not light leaking through the viewfinder on the camera , it's a more common problem.

There's a cover for it on the camera strap.

[Thalestris24]

Are you sure it's not light leaking through the viewfinder on the camera , it's a more common problem.

 

There's a cover for it on the camera strap.

Hi

Not in my case! I have a ccd... Light definitely leaks in through the mirror end but it probably wouldn't matter in normal use i.e. in the dark.

Louise

[lensman57]

Are you sure it's not light leaking through the viewfinder on the camera , it's a more common problem.

There's a cover for it on the camera strap.

It is not the viewfinder for sure, I was using an Atik428EX. I am now looking at the focuser too. I image from my back garden with street lights and the neighbours security lights causing havoc, so any llight leaks will show up on all the subs. I have wrapped the mirror end up with a black bin bag folded twice but it is an ungainly sight.

A.G

[Uranium235]

Ive been covering up my bottom (of the newt!) ever since I had the 130 (and the 150 previously). If you have enough ambient light at your imaging location, it will leak in through the bottom of the tube and give you a gradient. It seems all the PDS range have this "open bottom" design, but its easy enough to make a cover. A bit of circular card with notches cut out for access to the collimation screws, and just held on with a bit of tape - took all of 2min to make, saves much hassle.

Edit: Same applies if you have a manual filter wheel - make a cover for it, or a drawstring bag.

Edited April 5, 2014 by Uranium235

[Nillchill]

I have noticed the same with my 150pl , if you look down the tube in daylight , you will be surprised how much light bleed is there. Also I have noticed that the seam at the base of the tube bleeds light into the tube. I have found that a bit of tape on the seam has helped as has the fan plate I have fitted to the base.

Good luck in booking it all

[lensman57]

Ive been covering up my bottom (of the newt!) ever since I had the 130 (and the 150 previously). If you have enough ambient light at your imaging location, it will leak in through the bottom of the tube and give you a gradient. It seems all the PDS range have this "open bottom" design, but its easy enough to make a cover. A bit of circular card with notches cut out for access to the collimation screws, and just held on with a bit of tape - took all of 2min to make, saves much hassle.

Edit: Same applies if you have a manual filter wheel - make a cover for it, or a drawstring bag.

Thanks for your practical advice, the bottom cover is already prepared and yes while I was using a manual filter wheel I had the same problem and used to wrapp it up but nowadays I use an automated filter wheel so at least that side of the equation is covered. I am just a bit surprised that a range of scopes promoted and optimised for imaging should sufffer from light leaks where a simple plastic cover from the manufaturer would have helped to avoid all these problems. Now I have a Quattro 8s and the real fun begins.

Regards,

A.G

Edited April 5, 2014 by lensman57

[Uranium235]

I think the open bottom design with these telescopes is to aid cooling, but with CCD imaging being more demanding and the likelyhood that you are chasing very dim targets means that the gradients caused by this design come into play when youre trying to sort out your nebulosity from your gradient(s).

Good luck with the Quattro, it would be interesting to see whether you get a flat field out of the box (or with minumum tweaking).

[lensman57]

I think the open bottom design with these telescopes is to aid cooling, but with CCD imaging being more demanding and the likelyhood that you are chasing very dim targets means that the gradients caused by this design come into play when youre trying to sort out your nebulosity from your gradient(s).

Good luck with the Quattro, it would be interesting to see whether you get a flat field out of the box (or with minumum tweaking).

Thank you, as you mentioned the gradients started showing up once I got into the 1200s sub imaging. Hope this quattro fares better than the 150PDS, atleast the focuser seems to have been beefed up.

Regards,

A.G

[TomBee]

I'm using the 150PDS and there are some obvious light leaks from the primary mirror mount.
As earlier stated this design helps to cool down the mirror and tube quicker.

I always use a soft elastic cap before I start a session to minimize this problem.