defective 5x DIN?

[cpsTN]

Recently received a 5x DIN Achromatic Objective (NA 0.10/160mm) to replace my 4x (NA 0.10/160mm). There isn't enough travel distance for it to focus. It focuses when held by hand, though. It's so close to the 4x, you'd think it would focus. Is this common? I've contacted the seller.

[lorez]

You are probably trying to replace a non-DIN objective with a DIN objective.

lorez

[cpsTN]

If I am, it was mislabelled. That does make sense though.

[Oliver]

1. Could it be that the focus lock lever of your microscope (if it has one) prevents the full focussing? it can be found next to one of the coarse focus knobs.
2. Some microscopes allow for the adjustment of the focus travel with a screw. this is to prevent the stage from crashing into the objective. maybe it is set to block further focussing.

Oliver

[apochronaut]

In your intro. you referred to the 5X as a D.I.N. objective but you did not describe the 4X as such. Your D.I.N. objective should focus close to 45mm from the surface of the nosepiece port to the subject. If your other objective is not D.I.N. , this distance will be different; as little as 33mm or thereabouts. THis would mean that you would need to back the focus off another 12mm or so to get the D.I.N. objective to focus. AS Oliver pointed out, a locked focus stop may be preventing the microscope from doing this, or it may just have not enough focus travel. On some microscopes too; you can move the stage in a slide, thus changing the focus range independent of the travel. By doing this you may be able to find a place where you can accommodate all your objectives, within the microscopes focus travel.

[75RR]

This quote is from this article: http://www.microscopy-uk.org.uk/mag/ind ... ompat.html by Robert Pavlis

"This means that 160mm and 170mm tube length objectives can be interchanged between instruments, regardless of the manufacturer. HOWEVER, objectives vary in the distance between the face of the nose piece and the plane of focus! The RMS standard is 31mm, the JIS (Japanese) standard is 36mm, and the DIN (German) standard is 45mm. It is EXTREMELY undesirable to have a microscope that has objectives that are not all of the same standard."

The reason for this is that you loose parfocality, the ability to switch objectives and maintain the subject in focus with only minor fine focus adjustments. Apart from the considerable inconvenience of having to refocus from scratch when switching objectives, lack of parfocality can very easily lead to shattered cover slips and slides and consequently damaged objectives.

[billbillt]

Personally don't trust parfocality in general... I always back away from the slide a lot to index, then refocus... The extra second of time spent to do this means little to me... I am not in any hurry for sure..

BillT

[75RR]

Personally don't trust parfocality in general... I always back away from the slide a lot to index, then refocus...

If you have mixed objectives then your procedure makes sense.

[billbillt]

Personally don't trust parfocality in general... I always back away from the slide a lot to index, then refocus...

If you have mixed objectives then your procedure makes sense.

It is just my preferred way of doing things.. we all have different ways...

[zzffnn]

OP: Oliver and apochronaut said it all.

Importance of parfocality depends on your application and budget.

For fast moving live subjects, high power/NA and short working distance, I prefer remaining parfocal.

But in reality, remaining parfocal can cost a bit more if the objective you want is rare/expensive and short. So for non-moving subjects, low power (<= 20x objective or up to NA 0.65) and/or long working distance, I mix short and long objectives sometimes. If cost is no issue, then I prefer remaining parfocal.

[cpsTN]

The 4x is DIN, as it is the original to the scope.

[cpsTN]

Hey guys. I adjusted the travel distance enough for the 5x to focus with all the EPs, but without moving too far up. All seems to be well. Oliver was right; it was a screw setting.