Testing the eyepieces for dirt with pinhole imaging

[j.gardavsky]

Hello all,

back in the days on the blue forum, I have been talking about testing the eyepieces, and here we are.

Th pinhole imaging is an easy tool to check out the optics for dirt and other blemishes, coming from the manufacturing, and from the later use.

The method is trivially easy, it comes from the elementary science of optics.
Take a needle, and make a hole.
In the case of an eyepiece, it is strightforward to take the old Kodak film barrel, and to make a small hole into its bottom,

Then, you will hold the canister with the pinhole in front of the EP thread, and look through the EP against the bright skies.

Now, the next pic shows 2 situations, I have observed on 2 different eyepieces,

The bubble in the glass of one of the lenses comes from missing QC in the manufacturing process of the glass material melting,
and from the missing QC of the final product (eyepiece) - they should have seen it, ha, ha.
The dirt is a residual after not completed cleaning, nicely visualized with the pinhole imaging.

Thank you for reading and looking,
JG

[Lady Fraktor]

An excellent way to check your eyepieces!
Thank you for posting this JG.

[Michael131313]

Thanks very much for a great idea, JG.

[DeanD]

Thanks JG, a great way to check things out. (Although, could this be the eyepiece equivalent of shining a torch on a mirror? )

I had an air bubble in the centre of a brand new TV 19mm Panoptic: but it was big enough to see easily without the pinhole... Friday afternoon manufacture and/or QC? Needless to say, it went back from whence it came.

All the best,

Dean

[Don Quixote]

Very nice JG.
Thank you for this tip.

[j.gardavsky]

Thanks JG, a great way to check things out. (Although, could this be the eyepiece equivalent of shining a torch on a mirror? )

I had an air bubble in the centre of a brand new TV 19mm Panoptic: but it was big enough to see easily without the pinhole... Friday afternoon manufacture and/or QC? Needless to say, it went back from whence it came.

All the best,

Dean

Hello Dean,

they buy the glass materials which have not passed the QC for the cameras optics in the smart phones, just my guess.

Have you ever got an eyepiece with the "QC passed" sticker ?

You have squared the bubble right,
JG

[bladekeeper]

Thanks for this great tip, JG!

[Thefatkitty]

Thanks JG! Brilliant thought that I never would have thought of... Now I'm almost scared to see what I'll find!

All the best,

[bladekeeper]

Thanks JG! Brilliant thought that I never would have thought of... Now I'm almost scared to see what I'll find!

All the best,

Whatever you do, don't point the pin hole at your wife!

I almost ate a Telrad once after point it at her and making pew pew pew noises.

[Thefatkitty]

Thanks JG! Brilliant thought that I never would have thought of... Now I'm almost scared to see what I'll find!

All the best,

Whatever you do, don't point the pin hole at your wife!

I almost ate a Telrad once after point it at her and making pew pew pew noises.

That is so funny! And of course, now that you've planted that seed... I'll let you know how that works out and what a RA finderscope tastes like

Pew pew pew...