1. Field of the Invention
This invention relates to an ophthalmic photographing apparatus having the function of correcting the photographing light amount.
2. Related Background Art
There is known an ophthalmic photographing apparatus which can select film or a television camera as a recording medium or an image pickup element for imprinting the image of the fundus of an eye to be examined and can set a proper photographing light amount conforming to the recording medium during photographing.
Also, in a retinal camera, the reflectance of the fundus of an eye which is an object to be photographed differs greatly from one examinee to another and further, there is included in the eye a portion such as Macula or Disk of which the reflectance differs as much as several times to several tens of times from an ordinary region and therefore, in the case of a low reflectance like that of a lesion portion, it is necessary to effect the fine correction of the photographing light amount conforming thereto. There is also known an ophthalmic photographing apparatus having the function of effecting such correction of the photographing light amount.
Also, by combining a light amount conforming to a recording medium and the light amount correcting function, it becomes possible to effect photographing always at the appropriate exposure amount in spite of any variation in the recording medium and any variation in the reflectance of the fundus of the eye. As such light amount correcting function, there is known one having a predetermined light amount correction width and a predetermined photographing light amount correction stage.
However, the light amount correcting function of the above-described example of the prior art has only a variation in the photographing light amount as the standard and does not take into account the .gamma. characteristic of the recording medium and the difference in the dynamic range, and this gives rise to the problem that even if the photographing light amount correction width and the photographing light amount correction stage are optimum for a certain recording medium, the photographing light amount correction width is too rough or the photographing light amount correction stage is unsuitable for another recording medium and therefore the photographing operation becomes difficult and the original light amount correcting function cannot be achieved.