My Lunt B600 CaK diagonal anatomy and spectral curves

[sullij1]

Thank you Mark for another one of your eloquent answers. That's why I ask ya!

[mdwmark]

I said magenta, but I looked at an etalon and it was more light blue.
Mark W.

[marktownley]

To answer sullij question. I use a Dow Corning grease. Greases and oils like Cargille index matching oils work well. You can even use immersion oil that you use with a microscope. But they need to be sealed. You can use optical adhesive like Norland Products. Most of there's are UV cured. But they do make some that are not. They also have epoxy's for optical couplet. The advantage with the grease or oil is that you can take them apart if needed. The adhesive once it is cured that it.

Hi Mark. Thanks for this. Do you have a link you can give for the optical coupling gels please. I have had a good google around but wasn't really sure what I was looking for.

[marktownley]

I also want to point out when you are looking at bandpass filters you need to take inconsideration how it is put together.
If you look at the add in Edmund for bandpass filters. It has a hard coated and a standard design. What it doesn't tell you is that a standard design in meant for energy not visual. From the scan of the narrow bandpass you can see that it turn back on before 500nm. So you use a ITF to block it to at least 1000nm. In a standard design the two filters are cemented together. So you have two mirrors facing each other. Unless they are perfectly parallel you are going to create internal reflection that you have no way to get rid of.
Now if the bandpass is made so that all the coating are on one surface and the colored filtered glass is cemented on the back then you just tilt the filter like before.
Bandpass filters that are blocked to 800nm-1000nm maybe of this type. Any that are blocked to the Far IR in a cell are the first type.
This is why the ITF and the bandpass are on separate substrates.

I think this is a key point Mark in the ghosts / reflection issues that we have been observing, certainly food for thought for us all...

[dvmak]

Hi Mark,

Thank you for input.
Could you please give a link to the sale for 70$ for a 25mm filter?

[marktownley]

I'm not convinced the sale is on anymore on these, not in the UK anyway...

[Bob Yoesle]

Could you please give a link to the sale for 70$ for a 25mm filter?

Are these the filters you are referring to as being on sale (Anchor is a division of Edmund Optics)?:

http://www.anchoroptics.com/catalog/product.cfm?id=567

Note on these unmounted 394 nm 10 nm bandpass filters blocking is stated as "OD = 3.0, X-ray to 1.2μm," whereas the more expensive mounted hard-coated 394 nm 10 nm bandpass is "OD4 200-1200 nm."

http://www.edmundoptics.com.tw/optics/o ... ers/65-131

Bob

[Valery]

Could you please give a link to the sale for 70$ for a 25mm filter?

Are these the filters you are referring to as being on sale (Anchor is a division of Edmund Optics)?:

http://www.anchoroptics.com/catalog/product.cfm?id=567


Bob

Too bad transmission at the 393nm.

From the site description:

Blocking: OD = 3.0, X-ray to 1.2μm
Min. Peak Transmission: 334-400nm CWL = 25%
405-647nm CWL = 40%
650-1064nm CWL = 50%

[Bob Yoesle]

Yeah, I noticed that too Valery. But on the other hand, if the scatter is due to over saturation of the CCD sensor, less light and a longer exposure may be what we need to fix it:

Smear Explained

On the interline transfer CCDs used in many Point Grey cameras, each pixel consists of a light sensitive area, called the photosensor, and a light-shielded area, called the vertical transfer register. The vertical transfer register is used to shift the charge out of the photosensor and off of the sensor. Although vertical transfer cells are approximately 100,000 times less sensitive than the light sensitive region, photons may still tunnel into this area, especially when exposed to very bright light. This tunneling, or leaking, is the source of smear.

During image readout, image pixels are shifted vertically downard, row by row, through the vertical transfer cells to the readout register. If there is any leakage of charge into an area of the vertical transfer register, it will be picked up and shifted downward, so that every pixel above and below the area will contain this extra charge. The result is a relatively bright vertical stripe across the entire image.

Effect of Integration Time and Lens Aperture on Smear

Smear is often more noticeable when using very short (microsecond) shutter times. This is because the amount of charge collected in the light-sensitive area of the CCD varies based on exposure time, whereas the amount of charge that collects in the vertical transfer register is based on the sensor readout rate, which is a constant. With short exposures, the ratio of time integrating in the photosensor to time integrating in the vertical transfer is reduced. This reduced ratio may exacerbate smear.

Another factor that affects smear is the angle that light hits the sensor. Many CCDs use on-chip microlenses that cover each pixel in order to increase sensitivity. When light hitting the sensor is not highly collimated (which is often the case with wide angle lenses), light can be refracted by the outer edges of the lens in such a way that it hits the light-shielded portions of the CCD.

Reducing Smear

Smear may be addressed by reducing the source of bright light hitting the sensor, reducing the aperture, and using a lens that more effectively collimates light. Other, more specific, measures for reducing smear include the following:

Increase shutter (integration) time. This will increase the amount of time light is collected in the photosensors relative to the time in the vertical transfer register.

Bob

[swisswalter]

Yeah, I noticed that too Valery. But on the other hand, if the scatter is due to over saturation of the CCD sensor, less light and a longer exposure may be what we need to fix it:
Bob

Hi Bob

thank you very much. I guess thats it we should look for. I'm down to 0,4 ms exposure time . I guess 5 to 15 ms should be o.k.

[marktownley]

I'm just uploading some videos to youtube... There may be a different explanation...

[swisswalter]

Hi Mark

thank you very much for your anouncement. Wating for the link

[marktownley]

oops, sorry, I put it in the cak pst mod thread

[swisswalter]

Hi Mark

no problem, found it

[mdwmark]

The blocker that I said was $70 was just on Edmunds catalog online. I went to bandpass filters and it had them on sale.
The grease I use cost to much and it comes in 1# jars. Before Dow came out with there grease we used Cargille Immersion oil type A.
You can find it at Cargille.com. They make small amounts that doesn't cost much. The only problem is it is sticky and to clean it off the glass you need something like paint thinner. We uses Toluene but I don't think that a good idea any more. Xylene is a better choice. Lately I tried just mineral oil, it doesn't smell and it seem to work. Then Acetone , then alcohol to finish.
Norland Products web is www.NorlandProducts.com. and Andover sell an epoxy that they use. I am sure you could find other epoxy's like Andover uses.
Using the wrong designed filter.
Andover had sent me a batch of blockers that they had cemented together. So I couldn't take them apart. So I tried them in the optical stack. Everyone had problems with small secondary reflection. It ranged from only a small extra lim to a half the reflection of the solar image. They all got sent back.
If you are using hard coated filters with out an AR on the back then(like before you don't want to attach anything to the AR surface except air space), make sure you are on the glass side. If you oil/grease/epoxy the coated side you will drop the transmission of the filter.
Just a little more information
Mark W.

[swisswalter]

Hi Mark W.

thank you very much for the additional information

[marktownley]

Yes, thanks for the info Mark. All the filters i'm working with are AR coated, so not sure how I could use the immersion oils...

Here are the trouble some reflections if you have any suggestions as to their origins (and cure!) http://solarchat.natca.net/viewtopic.ph ... 50#p123619