Scratched SCT corrector plate, How will it affect images?

[DynaPB]

Hi, I'm looking at a Celestron NexStar 5 that has scratches on the Corrector Plate.

I am attaching a couple pictures of the scratches.

How do you think those scratches will affect the images seen through the scope?  Would it be unwise to purchase?

Thanks for the help!

Pete

[Cosmic Geoff]

It is unlikely to make any visible difference. They still work with slight dew on the corrector plate and that big round thing in the middle. 🙂

The practical effect will be to scatter some light and reduce the contrast.  

But if it is not yours, you could pass on it and look elsewhere. Lots of these have been sold so there are plenty other SCTs out there.

On the other hand, if you sense a bargain, see if the owner will accept a low offer.  They usually sell used for far less than the new price anyway.

 

[rl]

It looks terrible but the real optical effect is often not great in these cases. Provided whatever made the scratch has not affected the figure it's probably very serviceable. The actual area involved is miniscule compared to the whole plate. It might add some strange diffraction pattern if you look hard.

I'd be as worried about the iffy cleaning stains as the scratch, but that may look worse than it really is due to the illumination.

Can I see water stains around the screws holding the corrector in place? Might be worth looking for other signs of damage. 

If you want to change the corrector plate, I believe they have to be matched to the primary which might be an issue if still true.

I would expect the seller to allow some sort of return agreement allowing you to try it out first. 

When (if?) you sell it on, it will have a big effect of the price. People do expect clean optics above all else. 

 

rl

[dweller25]

It looks bad but it will have very little effect visually or imaging wise as it’s so far out of focus

Resale price is affected but I would buy it if the price was right

Edited November 17, 2023 by dweller25

[bosun21]

As has already been said that it won't be a major impact on the views but to me the question is how much is the seller asking for? With the defects the price should be a chunk lower than an equivalent one without the scratches.

[Oddsocks]

I don’t have any first-hand experience of this particular model and maybe it’s normal, or just an artefact of the way the photo’s were taken, but I’d be a little suspicious of the (apparent) missing section of “O” ring/gasket seal surrounding the corrector plate on the right-hand side, from the letter “U” in the “Multi-Coated” text extending down almost to the bottom of the plate.

There is a smaller gap in the “O” ring gasket on the left-hand side by the “mm” letters for the focal length specification, which may or may not be normal.

Without being able to compare to an untouched model I’d be a little suspicious that the corrector plate had been removed for cleaning and the “O” ring/gasket had broken or crumbled away leaving some large gaps.

Maybe someone here has owned one, or still has one, and can comment further?

[John]

11 minutes ago, bosun21 said:

.... With the defects the price should be a chunk lower than an equivalent one without the scratches.

Agreed - a big chunk lower. 

 

[DynaPB]

Thanks for the many great comments and suggestions!

I am close enough that I can go look at it, I might do that.

[Bugdozer]

2 hours ago, Oddsocks said:

I don’t have any first-hand experience of this particular model and maybe it’s normal, or just an artefact of the way the photo’s were taken, but I’d be a little suspicious of the (apparent) missing section of “O” ring/gasket seal surrounding the corrector plate on the right-hand side, from the letter “U” in the “Multi-Coated” text extending down almost to the bottom of the plate.

There is a smaller gap in the “O” ring gasket on the left-hand side by the “mm” letters for the focal length specification, which may or may not be normal.

Without being able to compare to an untouched model I’d be a little suspicious that the corrector plate had been removed for cleaning and the “O” ring/gasket had broken or crumbled away leaving some large gaps.

Maybe someone here has owned one, or still has one, and can comment further?

I have a 5se and I just had a look. Mine has exactly the same gaps, although they're not quite in the same places, they're rotated round. 

[ollypenrice]

SCTs have a low resale value at the best of times, compared with most other types of scope. Although this probably won't affect the view, it will massively affect the resale value. I don't know what a used C5 goes for these days but, whatever it is, I would not pay more than a third of that price for this one.

Olly

[Bugdozer]

3 hours ago, ollypenrice said:

SCTs have a low resale value at the best of times, compared with most other types of scope.

Why is that? Is it because they tend to get more problems, being a complex design? 

[Cosmic Geoff]

1 hour ago, Bugdozer said:

Why is that? Is it because they tend to get more problems, being a complex design? 

It is said that people buy them expecting to be able to capture fantastic deep-sky images, and then find it is harder than they thought.  Or some think new SCTs are over-priced.

[ollypenrice]

1 hour ago, Bugdozer said:

Why is that? Is it because they tend to get more problems, being a complex design? 

I suspect that it's because they were massively advertised at one time, and over-sold to boot.  The manufacturers pushed them for deep sky imaging when, in reality, they were pretty poor for this and people wanting to go into imaging sold them and went for alternatives. The arrival of the tiny-pixel DS camera has made their long focal lengths even less attractive.

I don't think they give much trouble. I've had four and all have been perfectly reliable. The spherical primary is easy to manufacture and collimation is simple. The long FL is restrictive but they are pretty nice as long as this is accepted. In a nutshell I just think they are too numerous and not suited to DS imaging.

Olly

[Knighty2112]

Looks like they took the photo with a flash. As we all know who have sold on any scopes that pointing any camera with a flash on to take a photograph down even the best of scopes makes it look like it’s been used as a coal scuttle! Doubt it will have any affect on views, and with carefully cleaning might come up as new with baader cleaning fluid and cloth. 

[bosun21]

No amount of wonder fluid can remove those scratches.

[Bugdozer]

1 hour ago, ollypenrice said:

I suspect that it's because they were massively advertised at one time, and over-sold to boot.  The manufacturers pushed them for deep sky imaging when, in reality, they were pretty poor for this and people wanting to go into imaging sold them and went for alternatives. The arrival of the tiny-pixel DS camera has made their long focal lengths even less attractive.

I don't think they give much trouble. I've had four and all have been perfectly reliable. The spherical primary is easy to manufacture and collimation is simple. The long FL is restrictive but they are pretty nice as long as this is accepted. In a nutshell I just think they are too numerous and not suited to DS imaging.

Olly

I would agree that if I was buying a scope specifically for imaging faint objects, it's not what I would go for. The long focal length is great for visual planetary and lunar observation though. 

[Starflyer]

I'd be looking at paying ~ 20% of new value, and bear in mind it'll be extremely difficult to sell if / when you want to upgrade.