Auriga - WideField with 50mm

[kirkster501]

85 x 80s ISO 1600 at F4.5.  50mm "nifty-fifty" on Canon 1100D. 17 Jan 2020 when directly overhead.  10 x bias, darks and flats each.

How to get rid of the flare on the brightest stars?  Any ideas please?  Also the red circle to the upper left of Capella ?????

[Laurin Dave]

Nice one Steve..  an appropriately sized filter step down ring will I believe get rid of the diffraction effects of the lens's iris (not done it just read it somewhere)

[happy-kat]

Step down rings can be used to reduce aperture rather then use the camera's iris this would prevent defraction spikes as mentioned above.

I love wide field.

Is your 1100d modded?

Edited January 18, 2020 by happy-kat

[MarsG76]

Nice photo....

 

[kirkster501]

Hi guys, thanks.  Yes it is a modded 1100D.

I have seen these step down rings.  So you leave the camera wide open and step it down with a ring/  Can you stack these rings one on top? 

Mean to say this was made using a Star Adventurer, a might fine piece of gear indeed.

Edited January 19, 2020 by kirkster501

[tooth_dr]

Nice image Steve, flaming star and tadpoles shoeing well.  I want to use step down rings too to go from F2.8 to F4.0 but not sure how to work out what size.

[Laurin Dave]

They screw into the filter thread and come in different sizes to fit different lenses..   if your lens is 55mm and say you want f5 then the required aperture in mm is 55/5.0 ie 11mm (maths simple for this one!)   

[happy-kat]

Is that a 11mm total reduction to get f5 on a 55mm lens, so a 55mm to 44mm stepdown ring? Or an I doing that wrong?

EDIT, nope that's not right I've done it wrong

Some refection later I thinks it's lens length divided by aperture. I need some stepdown rings as well.

 

Edited January 19, 2020 by happy-kat

[The Admiral]

From Wiki:

"The f-number of an optical system is the ratio of the system's focal length to the diameter of the entrance pupil ("clear aperture"). "

So here:                                    f-number = FL/D

So, for f/5 with a 55mm lens

                                                 D=55/5

Therefore,                               D=11mm

and for f/4                              D=13.75mm

Well, in theory! I guess it'd be instructional to check that the diameter of the front element does fit this formula for the designed lens aperture too.

Ian

Doh, I think I've got that right now, how many edits have I had to do .

Edited January 19, 2020 by The Admiral

[kirkster501]

Hi,

So do you stop down with these threaded step-downs into each other (the bottom one screwed into the lens) to stop it down to the required level to reduce the spikes?

Also, if you look at my picture (crop below)  there is a strange halo effect with bright stars and this halo is radially away from the optical centre of the 50mm lens.  What is that please?  Is it a by-product of a cheapish lens?

[kirkster501]

https://www.amazon.co.uk/gp/product/B0786D35CQ?pf_rd_p=f20e70b1-67f9-48d1-8c78-ba616030b420&pf_rd_r=MQ11F3YSVNHH6HCNJ3B5

 

Are these the rings?  I was expecting something that blocked more of the aperture....?  Or do they screw into each other?