Chip on lens? Dropped? ED80

[astro-erago]

Hello all,

I've bought an old 80ED that had supposedly never been used. It was in its original box etc.

There's *something* on the lens that looks white-ish. About 2mm by 3mm.

Looking through from the focusing end it's jet black... Apart from that it looks ok apart from one speck of dust - also black when looking through it.

What do I do?

Also, even though the focuser action seems smooth there's a slight 'up/down' to the knob as it's turned. I wonder if it's been dropped and the rod has been slightly bent. 

So I'm also worried about 'soft' lenses if that's the right terminology.

How can I check the integrity of the lenses?

Thanks in advance.

Context: I had an 8" dob about 5 years ago. Moon. Saturn. Jupiter. Star hopped to the great Hercules cluster. Failed to see Orion Nebula due to light pollution. I'm slowly gathering cheap gear together to hopefully dabble in a bit of astrophotography this winter.

[saac]

Can you upload a photograph.  Who did you buy it from  - commercial trader or private 2nd hand sale?  If it was from a commercial (reputable) trader you should be able to return it without any difficulty. 

Jim 

[astro-erago]

Here's the picture - looks like a nasty scratch to me. Gutted. Doesn't look that bad by eye. What do you think?

 

[astro-erago]

[Xilman]

Undoubtedly unfortunate.

However, it might be of negligible effect when using it. It might be worth trying it out before seeing if you can ask for a refund.

At least one professional telescope, the 2.7m at McDonald Observatory, is still in constant use despite the primary being shot seven times with a 9mm handgun at point blank range and then hit  several times with a hammer. The craters so formed produce a roughly 1% drop in light gathering and a minor amount of diffraction artifacts.

[saac]

As Xilman suggested , test it out first, most likely it will have no discernible  impact.  That said, depending on how much of a bargain it was and what was promised/described by the seller then you may feel inclined to ask for a refund.  If it were me, and I had purchased it at a good price, then so long as it tested ok visually I would live with it unless it was sold as good condition etc.  

Jim 

[astro-erago]

OMG yobbos! Well that's cheered me up a bit - funny - kind of.

That's a reflector though I assume... The light can come from other parts of the mirrors?

This is a refractor and there's a big black dot in the middle of the view. I think I might have a little cry.

[ollypenrice]

This is a new Celestron RASA 8.  Right in the middle of the corrector plate (the front optical elmement) it has... a large, cooled CMOS camera. Not a small scratch, a large and entirely opaque CMOS camera.

So you really don't need to worry too much about your scratch. It's good that it looks black from the rear because it shouldn't create any internal reflections, either.

I know it's nice to look at pristine optics but the truth is that grubby, marked optics give near-identical results. However, I'd bargain with vendor for a discount.

Olly

[astro-erago]

Thanks for the encouragement all.

But, and please excuse my ignorance if I'm wrong, your camera just reduces the overall light capture. And the gunshot holes in the big mirror...other parts of the mirror supply the light. This is lenses only, and so there's going to be an area of camera sensors that receive zero photons isn't there? Just like the black dot on the back of my eye?

[Xilman]

30 minutes ago, astro-erago said:

Thanks for the encouragement all.

But, and please excuse my ignorance if I'm wrong, your camera just reduces the overall light capture. And the gunshot holes in the big mirror...other parts of the mirror supply the light. This is lenses only, and so there's going to be an area of camera sensors that receive zero photons isn't there? Just like the black dot on the back of my eye?

Nope.  All of the lens in a refractor forms all of the image, just as all of the mirror does in a reflector.

You can test this easily enough with a telescope you don't treasure too highly (an old pair of binoculars perhaps) by cutting a small irregularly shaped piece of paper from the sticky portion of a Post-It note. Put it on the objective anywhere you like and look through the telescope. Repeat with paper in different places and with different sizes and shapes of paper. Clean up your test equipment afterwards, which shouldn't be too difficult because Post-It notes are designed not to be very sticky nor to leave much residue.

As for the Celestron, that big glass plate in the front, the one with the enormous obstruction in it, is a lens, like the one in the front of your telescope. It plays its part in forming the final image.

Edited August 10, 2021 by Xilman
Add final para.

[rl]

At least one professional telescope, the 2.7m at McDonald Observatory, is still in constant use despite the primary being shot seven times with a 9mm handgun at point blank range and then hit  several times with a hammer. 

Beginners take note; less risky collimation techniques are available...

Edited August 10, 2021 by rl

[astro-erago]

13 minutes ago, Xilman said:

Nope.  All of the lens in a refractor forms all of the image, just as all of the mirror does in a reflector.

You can test this easily enough with a telescope you don't treasure too highly (an old pair of binoculars perhaps) by cutting a small irregularly shaped piece of paper from the sticky portion of a Post-It note. Put it on the objective anywhere you like and look through the telescope. Repeat with paper in different places and with different sizes and shapes of paper. Clean up your test equipment afterwards, which shouldn't be too difficult because Post-It notes are designed not to be very sticky nor to leave much residue.

Awesome news. Thank you so much for the clarification.

I must have jumped to conclusions based on looking through it without an eyepiece.

I need to ponder on what the optics are doing - never had a refractor before.

I should have called my account "not-newton"

[StevieDvd]

If you have an eyepiece and a diagonal (plus a tripod/mount would be even better), then have a look at a distant object in daylight.

Another indicator of the view not being ruined is the use of bahtinov masks for focusing, yes it reduces the light intake but still gives you views of stars to aid in focusing.

Edited August 10, 2021 by StevieDvd
typos

[wulfrun]

Somewhere on the net (can't find it again though!) is a photo taken with a camera lens that had been dropped and the front element smashed. The lens was held together only because the pieces could not fall out. The photographs it takes are perfectly OK. I have a camera lens with a small chip that doesn't degrade the image. I blacked the chip with a Sharpie pen, which reduces the chances of lens flare (less problematic with a scope lens I'd guess).

As said above though, you shouldn't expect this unless you bought it "sold as seen" and you knew beforehand. However, use it and see if a real problem exists or not.

[astro-erago]

1 hour ago, StevieDvd said:

If you have an eyepiece and a diagonal (plus a tripod/mount would be even better), then have a look at a distant object in daylight.

Another indicator of the view not being ruined is the use of bahtinov masks for focusing, yes it reduces the light intake but still gives you views of stars to aid in focusing.

Yes it came with a 2" star diagonal and a 7mm orthoscopic eyepiece as well as the equivalent of an EQ5.

I'll set it all up and try it out.

Bahtinov mask arrives in two weeks... If you don't mind clarifying, how could that help in diagnosing issues? Are you referring to the potential soft lenses?

If I can get a decent star pattern can I crack a beer?  

[StevieDvd]

A good image in daylight and you can have a shandy & bag of crsips as well.

 

Edited August 10, 2021 by StevieDvd

[Ian McCallum]

On 10/08/2021 at 15:52, Xilman said:

Undoubtedly unfortunate.

However, it might be of negligible effect when using it. It might be worth trying it out before seeing if you can ask for a refund.

At least one professional telescope, the 2.7m at McDonald Observatory, is still in constant use despite the primary being shot seven times with a 9mm handgun at point blank range and then hit  several times with a hammer. The craters so formed produce a roughly 1% drop in light gathering and a minor amount of diffraction artifacts.

Edited November 21, 2021 by Ian McCallum

[Merlin]

I have a 8X42 Opticron binocular. One day, my screwdriver slipped  when  I was tightening a screw. It gouged out a small pit in one of the objectives.

The defect makes no noticeable difference to the optical performance because it isn’t in focus.