Refractor lens blemishes - what are they?

[bendiddley]

I have just purchased a second hand evostar 100 ED and it has some blemishes on the lens glass, see photos. Can anyone tell me what they are and how I can get rid of them? The two photos are taken with different light angles to show the two types of blemishes. Both images were taken under strong sunlight which exaggerate the appearance, they don't look as obvious under normal conditions and believe it or not, are actually not that noticeable unless you get the angle right.

[xtreemchaos]

id give it a clean first, when you shine a torch or bright light into a lens cell it makes anything look a lot worse than it is, unscrew the lens cell and have a better look and give both sides a clean if needed. charl.

[bendiddley]

Thanks Charl. I'll give that a go. Any advice on how to clean it?

[xtreemchaos]

badder wonder fluid is ment to be great, give both sides a blow with a rocket blower first to get rid of grit. but I use warm water on a cloth then a clean dry lens cloth to shine. charl

[kirkster501]

I would leave it well alone.  That will not make any difference to the scope whatsoever.  Each time you clean the objective you risk scratches.  That is a fare enough trade off if the lens is filthy.  But yours isn't...

[LightBucket]

I have cleaned my recent secondhand scope I bought an 80mm triplet, it looked a lot like that....mine was probably a bit worse.

It is probably dried tree sap mixed with dried dew, and dust.. make sure you use a BRAND NEW UNTOUCHED micro fibre cloth and the Baader wonder fluid, bent,y blow off and loose dust first then gently spray some fluid on the cloth and wipe over the lens complete once or twice and then leave a few seconds to dry...it will look mint afterwards, mine did, and the lens now looks new and completely unmarked...

The secret is to use a brand new cloth, as even if the cloth is touched with fingers it will leave a grease residue which will get onto the land and leave smears...trust me it works.. good luck

[bendiddley]

Thanks guys. I've have just cleaned it with baader wonder fluid. Cloth was a bit oily so used a new spectacles cloth as well and it has come up a treat! Many thanks!

[Alkaid]

Good to hear!  Looked like dried dew to me, or condensation from being brought back into the warm house straight from a cold night.  I learnt that lesson with a cheaper refractor - always bring it back up to temp slowly....ED100 has a case (hopefully you got one with it??) so if you take the case outside with you so that it becomes cold,  bringing the cased scope back inside with you at the end of the session will allow the inside of the case to warm up very slowly - result is no mist or condensation issues on the lens.

With my TAL (no case) I take it straight into a cool cellar when coming in and leave it there for a while....otherwise the lens would look like it had been in the shower  :-)

[ollypenrice]

According to Baader, who know what they're talking about, it is as well to clean refractors reasonably regularly (I'd call that 2 to three times a year) because some of the organic matter than can reside on the surface is able to damage the coatings. I'm far more reluctant to clean mirrors than lenses because lens coatings are very hard. Aluminium, however, is very soft.

Olly

[bendiddley]

Thanks guys!

[domstar]

@Alkaid What do you do with your ED100 if it has dew on it when you pack up? Do you leave it closed then dry it off in the morning or open it up when you get in?

Sorry, just read your post again and you're not talking about your own scope. So in that case what would you do?Thanks.

[Dave In Vermont]

I always feel the need to say:

Using a flashlight/torch on a lens/mirror will make your absolutely pristine optics appear as though the Battle of the Somme took place on it. So, for your sanity, only view these by means of natural, ambient lighting.

Honest!

Dave

 

Battle of the Somme

[Geoff Lister]

After a good observing session, the last thing you want is a room-full of moisture-rich warm air condensing on your optics; or any other parts of your telescope, including the electronics boards in powered mounts, handsets and cameras. You can limit the temperature difference, by moving the kit into an unheated shed or garage; and/or limit the amount of air that can flow past the kit by fitting end caps and placing everything in boxes or plastic bags.

Over the years, I have kept most of those little "Silica gel - do not eat" bags. They can be reconditioned by placing on a tray, and heating in an oven at about 120 deg C, for a couple of hours. In theory, it can also be done in a microwave oven, but as the gel dries out, there is less moisture to absorb the microwave energy, so it puts more strain on the magnetron. Once reconditioned, I store them in screw-top jars. If I am using my DSLR camera, at the end of the session, I put the camera, and a few of these bags, into a zip-lock plastic bag, and leave overnight. The "used" bags go into another screw-top jar, and when I have a tray-full they get reconditioned again.

Geoff

[Alkaid]

19 hours ago, domstar said:

@Alkaid What do you do with your ED100 if it has dew on it when you pack up? Do you leave it closed then dry it off in the morning or open it up when you get in?

Sorry, just read your post again and you're not talking about your own scope. So in that case what would you do?Thanks.

Hey domstar, no worries.  If the lens on my refractor was already dewed up when outside, I would still bring it inside to a cold room and leave the caps off at both ends overnight.  My house has a cellar that is typically just a few degrees  warmer than outside; so if the scope is not already dewed up, it won't dew up like a bathroom window upon bringing inside......and if it is dewed up beforehand, the slightly warmer temp will evaporate the existing dew without allowing any more condensate to form.

It's all about temperature differentials and keeping them to a minimum.  Warm the scope up slowly after use= no water inside.  But if dewing does happen on the lens during use- never cap a wet scope and leave it.  I did that once with an old scope thinking I would deal with in the morning and when I did the moisture had passed to the inside surfaces of the two doublet lenses....it evaporated but left very unsightly dew spots that could not be removed without lens disassembly....and no way was I wanting to do that....

And if you do the overnight thing and leave the scope uncapped at the lens end, make sure the other end is also uncapped so that each side of the lens might warm up at the same(ish) rate.

Perhaps I'm going a bit far really....but I do not like dew / water on my optics   Thank god I don't own a Mak (yet)   LOL

 

[domstar]

@Alkaid Thanks for such a comprehensive answer. I appreciate it.